The Anatomy and Physiology of the Organs of Respiration of Porcellio,
Cylisticus, Armadillidium, Ligidium and Oniscus.
Porcellio scaber L a t r e i l l e .
T h e general external anatomy and relations of dlie gills of Porcellio have been well de--
scribed by several of the authors above mentioned, especially L e r e b o u l l e t . It will be sufficient,
therefore, in the present work, as a preparation for an account of the histological anatomy of the
outer gills and the included corpora alba, to describe the outward appearance of a single gill.
The features presented by the inner surface of the first right outer gill of Porcellio scaber, male,
are as follows:
The general outline (Fig. 1) is that of a triangle with broadly rounded corners. Along
the anterior side which is slightly curved inwards is situated the articulation of the gill with the
basal joint (Art.). The inner side which lies contiguous to the stylet along the middle line of the
body is convex outwards; the lower two-thirds of its margin is beset with about 15 stout hairs.
The outer and posterior side forms an irregular line marked by a sharp angle directed inwards.
The face of the gill falls into two parts: the general part, making up more than one-half
of the whole and the special part which includes the corpus album. The general part is marked
by dots which along the margin are aggregated into a broad continuous line and elsewhere are
scattered or irregularly grouped. The marginal line of dots lies immediately contiguous to the
chitinous wall of the gill at the junction of the inner and outer faces.
The special part may be seen best by mounting a gill in water and examining under a low
power of the microscope with reflected light. In the outer portion is seen a whitish body presenting
the general appearance of a deuse clump of bushes. (Fig. 1, tr.). The base of the bushy mass lies
toward the angle on the posterio-lateral margin of the gill and the branches are arranged radiately
arount the base terminating in minute twigs. By focussing at different levels it becomes evident
that this body lies within the gill which in this region is much thicker than elsewhere. Since by
transmitted light the body appears dark, it may be inferred that it contains air. Furthermore,
by pressing upon the cover-glass a bubble of gas may be seen to pass out at the angular indentation
on the margin of the gill.
A portion of the wall of the gill overlying the white body shows very marked modifications
(Fig. 1, Gr. a). This portion has well defined boundaries, being included within a curved line, convex
inwards, lying at the surface of the gill, and two shorter curved lines, convex outwards, the
intersection of which forms the marginal angle referred to above. The surface of this region presents
the appearance of a net-work. The meshes of the net-work appear as dark lines under transmitted
light, indicating that they are furrows in the chitinous wall of the gill and contain air.
Minute Anatom y. Examined with a high power of the microscope, the several parts
just noticed present the following features:
The chitinous wall of the general part of the gill shows superficial markings, consisting of
minute pits which appear as dark points. They are arranged so as to form a pattern composed
of polyginal areas (Fig. 2).
The bodies referred to above as dots are seen to present the appearance of nuclei. They
lie immediately under the chitine and are of irregular sige and form. By focussing at different
levels it may be seen that associated with many of the nuclei are strands of tissue which extend
from the dorsal to the ventral wall of the gill. These form pillars and will be further described below.
In that portion of the special region of the gill where the wall presents the appearance
of a net-work the chitine is sculptured in a peculiar way. The surface in thrown into irregular
polyginal areas which are separated by furrows (Fig. 3b; P. a, Gr.). The areas themselves are
sculptured by much finer furrows, lying in short angular lines. The elevations and depressions thus
formed give the surface of each area the appearance of a pattern.
That the larger furrows or grooves separating the polyginal areas contain air may be demonstrated
by mounting a gill in water, when they are seen to appear white by reflected and dark
by transmitted light. If a gill is placed in alcohol before examining the net-work does not appear
dark under transmitted light. The finer furrows of the polyginal areas do not appear to hold air.
Underneath the chitine presenting these special modifications may be seen corpuscles which
here occur somewhat in accumulation. When pressure is applied to the cover-glass these corpuscles
move independently. Examination of a drop of blood taken from the body of a living animal shows
the same corpuscles present in the blood. They are of two kinds, namely: spherical, nucleated
cells and larger, highly granular, nucleated cells of irregular form. The former which are much
more numerous than the latter are the ordinary blood corpuscles; the latter are leucocytes.
The two forms of blood corpuscles may be seen elsewhere in the gill but occurring sparsely
as compared with the special region above mentioned. It w'ould appear that W a g n e r (see reference
p. 10) in referring to the “gouttelettes de la graisse“ and in stating that they occur aggregated
chiefly in one place in the gill had observed the corpuscles distributed as above described.
A portion of the marginal region of the white body presents an appearance somewhat resembling
a piece of branching coral (Fig. 5). The whole structure appears to be hollow, with smooth
thin walls. The appearance of irregular markings on the walls is probably due to shrinkage, consequent
upon the passing out of air.
In te r n a l Anatomy. Fig. 4 represents a cross-section of the gill taken in the direction
of the line s s' Fig. 1. The gill is seen to fall into two portions, a thinner and a thicker; these
correspond, respectively, to the general and special parts, described above. The chitinous wall (Ch)
is in general thicker‘on the lower or ventral side than on the upper or dorsal side. Within the
chitine is a layer of tissue with conspicuous nuclei — the hypoderm (Hy). The hypodermic layers
lining the two opposite chitinous walls are not entirely separated but, in the general portion of the
gill, are connected by extensions, forming pillars (PI.). The space crossed by these pillars is the