584 GEOFFREY SMITH. 
costracan, it inclines to the Kucaridan rather than the 
Peracaridan type. 
The first dorsal diverticulum to the gut is a thick- 
walled pocket which opens into the pyloric division of the 
stomach by two lateral passages on the outside of the lateral 
pyloric ridge (B). In the section shown in Pl. 12, fig. 4, 
only one lateral] opening is seen on the right side. 
The histological character of this diverticulum is extremely 
puzzling (Pl. 12, fig. 4). It consists of thick walls in which 
crowds of nuclei are densely packed without definite cell- 
outlines round them, and many of the nuclei are seen to be 
either actually undergoing mitosis or else in preparation for 
division. ‘his process of mitotic division is to be observed 
in fully grown adult specimens, so that we are evidently deal- 
ing with a tissue which remains in a permanently embryonic 
condition. There are no cells of a glandular nature in this 
diverticulum, as might well be expected from its position on 
the alimentary canal. 
It is impossible to do more than guess at the function of 
this remarkable organ, but from the active reproduction of 
the cells composing it, it may be suggested that its function 
is to supply new epithelial cells for the lining of the alimen- 
tary canal as the old cells wear out and become effete. 
Laterally the walls of the first diverticulum pass into the 
epithelium of the mid-gut or endoderm (Pl. 12, fig. 5). 
The portion of the mid-gut lying between the first and 
second diverticula is essentially glandular in nature, especially 
in the anterior and dorsal region. In this region the epithe- 
lial cells are tall and columnar. The majority of these cells 
have lightly-staining oval nuclei, but wedged in between these 
ordinary columnar cells are nests of much-flattened cells with 
spindle-shaped nuclei, which stain intensely with haematoxylin, 
These cells are apparently special gland-cells of some kind, 
which pour a secretion into the gut. Ventrally and posteriorly 
the lining epithelium of the mid-gut is composed of short 
cubical cells with rather darkly staining nuclei. 
The basement membrane of the mid-gut is remarkably 
