No. 384.] REVIEWS OF RECENT LITERATURE. 955 
which he considered to be glandular in function. Looss (93) argued 
that the cuticular layer arises by the migration to the surface of the 
body of a material set free in the vacuolization of the parenchyma 
cells. These he believed to be derived from the layer of submuscular 
cells, which he compared to a Cambrian layer in plants. A fifth view 
was put forward by Blochmann (96). According to his ingenious 
explanation, the outer body covering is a true cuticula secreted by a 
layer of epithelial cells which have elongated backward and come to 
lie beneath the layers of muscle fibres. They are more or less sep- 
arated from one another and connected with the cuticula only by 
narrow processes extending between the muscle fibres and compar- 
able with the ducts of gland cells. 
Apoblema is an appendiculate trematode, and it is upon the cutic- 
ular layer covering the caudal appendix that the observations of 
special interest were made. In the earlier part of its life, passed 
within the body of a copepod, the caudal appendix is present only in 
the form of an invagination of the posterior end of the worm forming 
the caudal vesicle. Later, when the animal becomes free living, the 
caudal vesicle becomes everted to form the caudal appendix. After 
this has taken place there is no difference to be observed between the 
cuticular covering of the appendix and that of other parts of the body. 
It is a typical trematode cuticula destitute of spines and divisible into 
two layers, an outer and a deeper one, as shown by differences in 
reaction toward stains. Immediately beneath the cuticula are the 
usual layers of muscle fibres, circular and longitudinal, and the layer 
of submuscular cells. In the appendix, however, the latter layer is 
absent. 
In the condition when the appendix is invaginated to form the 
caudal vesicle its cuticular layer is covered externally (toward the 
lumen of the vesicle) by a layer of columnar epithelial cells, over 
which is a delicate membrane —a true cuticula. In other words, in 
the caudal vesicle the layer which is later to become the cuticular 
covering of the appendix has precisely the relations of a basement 
“membrane. About the time that the vesicle becomes evaginated 
to form the appendix, the layer of epithelial cells separates from the 
cuticular layer upon which it rests. Evidence for this, Pratt found 
in the presence of shriveled epithelium in the caudal vesicle nearly 
separated from the underlying cuticula. 
This evidence from Apoblema furnishes strong support for the 
older theory that the body covering represents what was primarily a 
basement membrane. Pratt takes this view, but argues that the layer 
