The Anatom oyf Pentastomum teretius- culum (Baird).

82 Pages·2006·3.78 MB·English

The Anatomy of Pentastomum teretius-
culum (Baird).
By
W. Baldwin Spencer, M.A.,
Professor of Biology in the University of Melbourne.
With Plates I—IX.
DURING the summer of 1887-8 the Field Naturalist Club
of Victoria arranged for the annual collecting expedition of
its members to be made to King Island. The latter lies to
the west of Bass Straits, halfway between the mainland of
Victoria and Tasmania, and is a wild and, save for two light-
house keepers, uninhabited island. Whilst collecting we came
across very numerous specimens of the copper-head snake
(Hoplocephalus superbus), and in one of these my atten-
tion was drawn by my friend and pupil, Mr. B. Dombrain, to
the presence of a parasite inHhe lung, which proved on examina-
tion to be a large specimen of some species of Pentastomum.
Shortly afterwards I killed another snake of the same species,
and on cutting the body open found the lung to be crowded
with the same parasite. The weather was extremely warm,
and, as we were on the tramp, all that could be done was to put
the animal into spirits, and trust to finding the parasite again
for the purpose of watching it alive. This opportunity has
unfortunately not occurred, though since that time I have cut
open many "copper-heads" in the hope of finding the Penta-
stomum. Mr. D. McAlpine has been good enough to give me
four specimens of the same species of Pentastomum, which
VOL. XXXIV, FART I.—NEW SEE. A
2 W. BALDWIN SPENCER.
he has found in the lungs of a black snake (Pseudechys por-
phyriacus) in Victoria.
On searching through such literature as could be obtained
in Victoria I found that Dr. Baird had described a specimen
which was obtained in the mouth of a dead copper-head snake
in the Zoological Society's Gardens, London, under the name
of Pentastomum teretiusculum. Though the description
is somewhat incomplete, there can be no doubt but that the
form with which this paper deals is the one found and first
named by Dr. Baird.1
Since the time when Leuckart2 published his classic mono-
graph on the group—now more than thirty years ago—modern
methods of investigation have rendered it possible to study
more closely the minute anatomy of such, an animal as Penta-
stomum (where continuous sections are almost a necessity)
than could be done in earlier days, though to those of us who
now depend upon such methods the accurate and brilliant
results achieved by the older workers are a continual source
of admiration.
Despite the recent work of Hoyle,3 Lohrmann,4 Stiles/ and
Macalister,61 have thought it worth while to publish the fol-
lowing account of the anatomy of P. teretiusculum, which
has been made as complete as possible. In doing this I have
endeavoured to give (1) descriptions and figures of the ex-
ternal anatomy, (2) schematic representations of the structure,
1 'Proc. Zool. Soc.,'London, 1862, p. 114.
2 ' Bau und Entwickelungageschichte der Pentastomen,' Leipzig, 1860.
8 "On a New Species of Pentastomum (P. protelis) from the Mesentery
of Proteles cristatus; with an Account of its Anatomy," 'Trans. Royal
Society of Edinburgh,' 1883, with pis. xxvii and xxviii.
4 " Untersuchungen iiber den Anat. Bau der Pentastomen," ' Arch. f.
Naturgesch.,' 1889. I am unable to refer directly to this work; my knowledge
of it is based upon references thereto in Stiles' monograph.
5 "BauundEntwickelungsgeschichtevonPentastomum proboscideum,
Rud., und Pentastomum subcylindricum, Dies.," 'Zeit. f. wissen.
Zool.,' Band. Hi, Part 1, 1891, p. 83, Taf. vii and viii. This paper also con-
tains a full bibliography.
6 'Proc. Roy. Irish Acad.,' 2nd series, vol. ii, 1875-7, p. 62 : "On Two
New Species of Pentastomum."
THE ANATOMY OF PENTASTOMTJM TERETIUSCULUM. '3
and (3) descriptions and figures of the actual sections and
histological preparations, from a study of which the schematic
drawings have been deduced.
To students, and those who are engaged in teaching,
schematic representations of the most diagrammatic nature
are, it appears to me, of great service.
I am much indebted to my friend Mr. W. E. Hoyle for his
kindness in sending to me a copy of Leuckart's work, which
I was unable to refer to or procure in Australia, and also for
his kindness in supervising this paper whilst it was passing
through the press.
The structure will be dealt with under the following heads :
PAGE PAGE
1. Habitat . 3 6. Secretory organs . 21
2. External anatomy . 4 7. Nervous system . 33
3. Structure of the body-wal 9 8. Sense-organs . . 37
4. Muscular system 10 9. Reproductive organs . 39
i. Alimentary canal 15
1. Habitat.
The adult form lives in the lungs of the two snakes, Hop-
locephalus superbus and Pseudechys porphyriacus,
popularly known respectively as the " copper-head" and the
" black " snake. The former is very common in certain parts.
In King Island it was not unusual to kill perhaps twelve to
twenty in the course of one day's tramp through the scrub.
I have myself as yet only found the parasite in the lung of two
specimens, and have never seen it save in King Island. On
one occasion Mr. McAlpine found it in the lung of a black
snake killed not far from Melbourne.
In one copper-head, which to all appearances was perfectly
healthy and vigorous, and measured about 4 feet 6 inches in
length, there were no fewer than 129 specimens to be counted
in the lung and tracheal tube, of which some twenty were
males, the rest females, in various stages of growth.
Each parasite lives with the whole of the head buried deeply
in the lung wall, and adheres so firmly by means of its hooks
4 W. BALDWIN SPBNOEB.
that a considerable pull is necessary to dislodge it. When this
is done a definite cavity is left, corresponding in shape and
size to the parasite's head. Not one was found loose in the
lung, though the fact that Dr. Baird found his specimen in the
mouth shows that they must have the power of becoming free
and of movement. Like other parasites, this one seems to try
to leave the body on the death of the host.
2. External Anatomy.
(Figs. 1-5.)
The form of the body is that of an annulated cylinder,
bluntly rounded at the anterior and somewhat tapering at the
posterior extremity.
It differs slightly in form and much in size in the two sexes,
which can readily, as in other Pentastoma, be distinguished
from each other by the position of the opening of the repro-
ductive organs. During life the whole body is of a bright red
colour, as noted by Baird, the colour being undoubtedly due to
the blood sucked in from the lung of the host.
(i) The Female.—The specimens vary much in Bize, some
being very small and immature, measuring not more than 12
mm. in length, whilst a large mature specimen will measure
32 mm. in length and 5 mm. in greatest width. Save the
anterior end the whole body is annulate, there being
from sixty-five to seventy annuli present (sixty-six in the one
figured). Occasionally the annuli may be slightly irregular,
an incomplete one being wedged in between two perfect ones
(fig.l).
Each annulus consists of an anterior and a posterior portion,
and between the two is a slight ridge more or less distinctly
marked. This, as will be shown later, can be detected with
ease in longitudinal sections. The anterior part corresponds
to the annular part, and the posterior to the interannular, as
described by Hoyle. With a lens it can easily be seen that
the anterior part of each annulus is covered with a number of
spots crowded closely together, and showing no arrangement
THE ANATOMY Or PENTASTOMUM TERETIUSOULUM. 5
into definite lines. Such spots are absent on the posterior part
of the annulus.
The rounded anterior or head end of the body is not marked
by annuli, and its length is about five times the breadth of an
annulus.
Mouth.—In the mid-ventral line a little way in front of the
first annulus is a distinct papilla, somewhat triangular in shape
with the angles rounded off, the whole projecting slightly from
the surface. The papilla arises from a depression, and is
surrounded by a narrow groove, which is also roughly triangular
in general form. The apex of the triangle formed by the
groove points forwards : the posterior side is at right angles
to the long axis of the body (figs. 2, 5), and forms a slit leading
directly into the mouth; in fact, seen from the ventral surface
the mouth has simply the appearance of a slight swelling out
of the groove. The papilla corresponds to the structure to
which Hoyle gave the name of "oral papilla " in P. protelis,
which Lohrmann also described as the " Mundpapille," but
which Stiles in P. proboscideum states is to be regarded not
as an oral papilla, but as an " Oberlippe." Whilst there is no
doubt that it performs the function of an upper lip, it is equally
certain that it has the form of a very definite papilla; in fact,
"oral papilla" most aptly describes its appearance and structure.
In P. tseniodes such a structure is apparently absent, the
mouth being described by Leuckart as a wide and gaping orifice
of oval shape.
Hooks.—On either side of the mouth is placed a pair of
hooks. These are prominent structures, with sharp curved
protruding points, and bases sunken in special pits on the head
surface. The hooks serve for the attachment of the parasite,
and each, so far as the external anatomy of the animal is con-
cerned, consists of a strongly curved pointed portion and a
broader basal part. The depression in which the latter is
placed is bounded by a rounded elevated ridge of the external
cuticle i within this, upon the base of the hook, lies a second
one, which is prominently marked where it passes across the
anterior end of the depression and hook.
6 W. BALDWIN SPENCEB.
Papillae.-^These structures, varying somewhat in number
and arrangement, appear to be constant features in the anatomy
of the Pentastomidae. Their presence has been described in all
forms save P. protelis, in which Hoyle was unable to find
them, though there can be little doubt that he would have
detected them had his material been in a better state of pre-
servation. Even in well-preserved specimens they vary remark-
ably in distinctness.
The papillae can be clearly divided into two sets, which may
for convenience be described as (a) primary and (b) secondary.
(a) Primary Papillae (figs. 2 and 5).—These comprise
only two, and each of these forms a more or less prominent
elevation, lying a slight distance anteriorly to the depression
which holds one of the hooks placed nearest the mouth—that
is, one of the more posterior of the two pairs of hooks. In the
retracted state these papillae are scarcely noticeable, but at
other times they project markedly from the surface. Each
has, close to its apex, a minute opening, which serves as one of
the openings for the duct running forwards from the hook-
glands to be afterwards described. Though invisible in surface
view, each papilla bears one or more simple sense-organs placed
close to the opening of the duct.
These papillae are the " Tastpapillen" of Leuckart, and were
regarded by him as the homologues of antennae. Lohrmann
states that the head-gland ( = hook-gland mentioned above)
opens upon them; and Stiles, rejecting Leuckart's suggestion
of their homology with antennae, agrees with him in regarding
them as sense-papillae, and says that the head-gland opens to
the ventral side of the papillae. The anatomy of P. tereti-
usculum shows that we are dealing with a form in which we
find combined the features described singly by Lohrmann and
Stiles. The latter says, "Auf grund meiner Beobachtung
betrachte ich diese Papillen gleich Leuckart als Sinnespapillen,
finde jedoch keine Veranlassung sie als rudimentare Antennen
anzusehen." As will be shown soon, and as Stiles has already
pointed out in the case of P. proboscideum, sense-papillae
are present, related in position to the external pair of hooks, as
THE ANATOMY OP PENTASTOMUM TERETIUSCULUM. 7
are the two large ones now described to the internal pair, and
these again identical in structure with others having no claim
whatever to be regarded as modified appendages. It would
appear from the above that very probably this single pair of
papillae, which are directly homologous with the smaller
ones, has become specially modified and enlarged in connec-
tion with the external opening of the hook-gland, and that,
agreeing with Stiles, they are not to be regarded as modified
antennae.
{b) Secondary Papillae (figs. 2, 3, and 5).—These consist
of seven pairs of minute papillae, which appear under the lens
as small white spots on the dorsal surface. They are distri-
buted as follows:
(1) A pair close to the anterior end of the depression
containing the external pair of hooks (figs. 2 and 3).
(2) A pair placed somewhat posteriorly to the latter (3).
(3) A pair placed posteriorly to the latter and nearer to
the median line (4).
On the lateral surface:
(4) A pair, one placed to the outer side of each of the
external or outer pair of hooks (5).
(5) A pair, one placed on each side of the body in a line
with (4) and the lateral line of the body (6).
On the ventral surface:
(6) A pair, one placed on each side immediately in front
of the first annulus, and correspondin g in position
to the interval between the two hooks on either
side (7).
(7) A pair, one placed on each side in the first annulus,
and corresponding in position to the hook nearest
to the mouth (8).
In addition to the above, there can in some specimens be
detected what is apparently a line of minute papillae, of which
a pair is present on each segment for perhaps the most
anterior eleven. These are placed along what is called the
" lateral line," where the body-wall is slightly thinner than
elsewhere, and becomes on contraction of the animal thrown
8 W. BALDWIN SPENCER.
into folds. Similar ones are noted by Stiles as present in P.
proboscideum; but as in the latter, so in P. teretius-
culum, they vary considerably, the examination of some
specimens leaving no doubt that true papillae are present,
whilst the examination of others will leave equally little doubt
that we are dealing simply with structures due to the wrinkling
of the cuticle and body-wall. After careful examination I
have been unable to detect their presence in sections.
Reproductive Opening.—This serves at once to distin-
guish, apart from the size of the two, the male from the female
form. The opening of the vagina is placed on the mid-ventral
surface on the eighth annulus from the posterior end (fig. 1),
though the modified part around the opening may extend on
to the annuli next in front of and behind this one. The
opening itself is crescentic in shape, the hinder wall being
formed by the anterior part of a low, rounded, and swollen
cushion-like structure: the anterior wall is swollen and tumid.
The cuticle which lines the opening is thick and yellow
coloured.
The anus lies at the very posterior end, between the two
lateral halves of the terminal annulus, the cuticle passing in
from the exterior.
(ii) The Male (figs. 4 and 5).—In this the general form of
the body, the hooks, mouth, anus, &c., agree with the descrip-
tion given of the female; the chief differences of importance
are (1) the size and (2) the position of the reproductive
opening.
The length of a large-sized specimen is about 13 mm.; the
greatest width (which occurs just behind the head region) is
about 2 mm. Whilst the size of the male is so much less
than that of the female, the number of annuli is greater, the
average being about eighty-eight, the number varying within
one or two of this.
Reproductive Opening.—The position of this at once
distinguishes the male. It has the form of an oval opening
with a raised tumid margin, the whole being placed on the
third and fourth annuli in the mid-ventral line, and with the
THE ANATOMY OP PENTASTOMUM TEEETIUSCULUM. 9
long axis of the oval at right angles to that of the body.
Through the opening can be seen a ridge running across its
short axis, and corresponding to the ventral edge of the
partition between the two tubes leading down to the atrium
genitale; whilst on either side of this ridge, when examined
with a lens under strongly focussed light, can be detected
a minute rod-like body, which must be the ventral edge of
a special chitinous process, which serves, as will be afterwards
described, to open up the female aperture prior to the passage
of the cirrus itself.
Sensory Papillae.—The only variation in these, as com-
pared with the female, lies in the presence of an additional
pair of secondary papillee placed just in front of the genital
opening, one on each side (fig, 5, 9).
3. Structure of the Body-wall.
(Figs. 29, 31, 32, 51.)
Under this head will be dealt with only the cuticle and the
cuticle-secreting cells; the muscles of the body-wall will be
dealt with under the special head of muscles.
The Cuticle.—The whole external surface of the body is
covered with a layer of chitinous material of nearly uniform
thickness (average *015 mm.). This cuticle is continuous
with the layer which lines (1) the stomodaeum, (2) the proc-
todoeum, (3) the openings of the reproductive organs, (4) the
ducts of the excretory glands, and (5) the invaginations con-
taining the hooks. These are described under the sections
dealing with the organs with which they are connected.
Stiles has described and figured two distinct layers in the
cuticle, a thinner outer and a thicker inner one. In P.
teretiusculum there can be recognised a very thin external
layer, which takes stain more deeply than the main portion,
which rarely stains at all. Around each segment runs a
pointed ridge dividing the cuticle into a larger anterior and a
smaller posterior ring, the latter part of the segment doubt-
less corresponding to what Hoyle calls the interannulus.
10 W. BALDWIN SPENCER.
This ridge is formed entirely of the outer layer, and stains
deeply. In longitudinal sections it is very clearly marked
(figs. 27,29, R.).
The thick inner layer, which, save in the region of the ridge
just mentioned, forms almost the entire thickness of the cuticle,
shows in sections the presence of great numbers of minute wavy
lines, as if it were composed of very thin laminse—an appear-
ance which may, however, be due to the action of reagents
(fig. 51).
All over the head region and in the anterior half of each
annulus the cuticle is pierced by numbers of minute pores,
which form the stigmata, or the openings of very numerous
irregularly arranged glands. Each pore has a circular-raised
margin (fig. 31, st. gl.).
The Cuticle-secreting Cells (fig. 51, E.).—These form
a continuous layer immediately beneath the cuticle. Each
cell is columnar (the average length is "035 mm.), and each
has a somewhat rounded internal end, close to which is placed
a distinct nucleus. The cells do not form a columnar epithe-
lium in the ordinary sense of the term, since they are not
uniformly closely apposed, but spaces are left between them,
through which pass to the cuticle the ends of muscle-fibres
and of special strands of connective tissue (W). There can be
no doubt that their function is that of secreting the cuticle.
In addition to this, groups of these cells are specially modified
to form the stigmatic glands, the description of which is given
under the head of excretory structures.
4. Muscular System.
(Figs. 24, 28—30, 32, 39, 51.)
All authors agree in describing (1) a layer of circularly
disposed fibres, (2) a layer of longitudinally disposed fibres,
and (3) a layer of obliquely disposed fibres. In addition to
these, muscles are developed in connection with the alimentary
canal, the reproductive organs, and the hooks, which are some-
what differently developed in different forms.