546 
EDWIN S. GOODRICH. 
produced the anterior extremity of the notochord, and the 
lateral outgrowths which give rise to the first pair of somites 
or anterior premandibular cavities of Balfour. In spite of the 
doubts raised by Hatschek (6) and von Kupffer (7), it is now 
generally admitted that the proboscis cavities of Balano- 
glossus, the anterior sacs of Amphioxus, and the preman- 
dibular cavities of Craniates are all homologous structures 
•representing the first pair of coelomic somites (Willey (15), 
MacBride (11)). 
No satisfactory explanation of the origin of the hypophysis 
has yet been arrived at. Beard, Dohrn, and others have 
suggested that it represents a vestige of the original mouth, 
a new mouth having been developed from gill-slits. But the 
fundamental correspondence in the structure and relations of 
the mouth and associated parts in the Ascidian, Amphioxus, 
and the Ammocoete larva, and many other facts which need 
not be mentioned here, render this view in the highest degree 
improbable. Many authors have sought in Amphioxus for 
the homologue of the hypophysis ; but, strangely enough, 
most of them profess to find it in the neuropore or olfactory 
pit of Koelliker. For this theory, suggested by Hatschek (6), 
and strongly supported by Willey (15), there seems to be no 
justification. Since both neuropore and hypophysis coexist 
in the embryo Craniate, are situated widely apart, and are 
related to quite different regions of the brain, it is difficult to 
see how they could correspond to the olfactory pit. On the 
other hand, the much more plausible comparison of the 
hypophysis with the wheel-organ of Amphioxus has received 
little attention. It is true that Legros at one time maintained 
that HatschelCs nephridium, Hatschek^s pit, and the wheel- 
organ correspond to the hypophysis and olfactory pit of 
Craniates (9) ; but this view was based, as already men- 
tioned above, on erroneous observations, and has since been 
abandoned. 
There is strong evidence to support the theory of the 
homology of the hypophysis with the wheel-organ of Amphi- 
oxus (the preoral pit of the larva). Were it not for tha 
