Cutaneous Glands in the Terrestrial Isopoda. 213 
one is obliged to create a particular technique in such work, 
for what succeeds in the case of other invertebrates—indeed, 
in one group of crustaceans—fails to give results. 
In working at the general anatomy of the Terrestrial 
Isopoda, I have been compelled to make numerous experi- 
ments with various media. Many have proved ineffectual, 
but a few have given excellent results, this enabling one 
to progress beyond the point reached by previous workers. 
The peculiar caudal or cutaneous glands are a case in point, 
and form the subject of the present paper. Hitherto their 
structure and distribution has remained only partially 
known owing to imperfect or faulty methods of preparation. 
These bodies are now described and figured in detail fora 
single species, viz., Porcellio dilatatus, Brandt, but practically 
all the British species of woodlice have been examined and 
partly worked out. At a later date I hope to give full 
details and figures of the distribution and __ histological 
structure of these glands in a large number of genera and 
species, together with some remarks upon their morphological 
significance—the present paper being merely a preliminary 
study, as expressed in its title. 
Historicat Review. 
The structures which form the subject of this paper were 
first described by Lereboullet in 1850 (5), who writes :—“ Up 
to the preseut no one has described the special organ of 
secretion in the woodlice. One knows, however, that these 
crustacea, principally the Porcellios, allow a flowing matter 
to escape from their caudal appendages, which recalls the 
silk of a spider, although much less consistent. 
“ Quite often, in touching the extremity of an appendage 
with the finger, one succeeds in drawing off a thread of two 
or three centimetres length and upwards ; as soon as it 
breaks it floats in the air like an exceedingly fine spiders’ 
web. 
“T have discovered the organs which are the seat of this 
secretion. They are small compound glands situated at the 
origin of the first articulation of the caudal appendages, in 
the most posterior part of the abdominal cavity on the sides 
of the rectum.” 
After briefly describing his method of preparation, this 
author continues :—“‘ These glands, numbering from four to 
six on each side, measure on an average ‘00 mm., they are 
composed of a variable number (about a score) of transparent 
vesicles of irregularly conical form; the contracted portions 
