MUSEUM OF COMPARATIVE ZOOLOGY. 85 
composed of three layers: an internal epithelial layer, composed of the 
flattened ectodermic cells with oval nuclei; a middle layer, composed of 
very much flattened cells, recognizable only by their long very narrow 
nuclei; and an external covering of mesodermic elements (Pl. IX. 
fig. 57). 
A few days before hatching a short tube is to be seen extending for- 
wards from the ventral face of the stercoral pocket to which it is joined. 
It is continuous behind with the part of the proctodeum which I have 
called the rectum, and in front it spreads out into a trumpet-shaped 
expansion which embraces the posterior portion of the yolk mass 
(Pl. VIIL. figs. 55,56; Pl. XI. fig. 70). The cells composing the epi- 
thelial lining of this portion of the intestine resemble more those of the 
stercoral pocket than those of the rectum. They are invested externally 
by a layer of flattened mesodermic elements continuous behind with those 
which envelop the stercoral pocket and the rectum, and in front with 
the mesodermic layer which invests the yolk. 
Schimkewitsch claims for the hind part of the alimentary canal in 
Epeira a very thin cuticular lining ; I have not been able to demonstrate 
its presence in sections of Agelena. 
From the dorsal wall of the pre-stercoral tube — just where it becomes 
confluent with the antero-inferior face of the stercoral pocket — the two 
malpighian tubes take their origin. The position of these tubes furnishes 
the only evidence that I have concerning the source of the pre-stercoral 
tube, and leads to the conclusion that it is of entodermic origin, and 
therefore a part of the mesenteron. 
I have not as yet traced the alimentary canal to its adult condition. 
At the time of hatching it is still incomplete, being composed of an 
anterior and a posterior portion, the inner extremities of which open 
towards each other by wide expansions, which abut directly upon the 
yolk. In the latest developmental condition that I have examined — 
about eight or ten days after hatching — the mesenteron is greatly ex- 
tended, and appears to be continuous at its sides with the yolk compart- 
ments of the abdomen. It doubtless is functionally active previous to 
this time, since there was a considerable amount of effete matter in the 
stercoral pocket. 
2. The Eyes. —It seems somewhat remarkable that up to the present 
time the development of the sense organs in the Araneina has been 
hardly more than touched upon. The meagre description by Claparéde * 
* Claparéde (’62, pp. 56, 67) is the only one, I believe, who has written anything 
about the development of the eyes, and he has given only an account of the exter- 
