288 Siisanna Phelps Gage 



p. 293 and compare Fig. 93, 6). The caudal diverticulum 

 of the sac many be compared to the thin layer in diemyctylus 

 forming the cephalic boundary of the diencephal (Fig. 6, 68, 

 52) then the remainder of the sac meets the requirements 

 of homology with the paraphysis of amphibia, — a thin 

 walled diverticulum from the caudal part of the pallium, 

 partly surrounded by bloodvessels and having the same rela- 

 tion to supracommissure and habenae. 



Balfour and Parker (3, p. 377) described in lepidosteus a 

 large sac which they say is homologous with Stannius' sac in 

 tlie sturgeon ; a similar one was described by Wiedersheim 

 in protopterus. Goronowitsch (21) has made the relations of 

 this sac very clear in the ganoid, and Burckhardt (8) in the 

 dipnoan brain. The conclusion with regard to the homology 

 of this sac, above deduced in the amia, is confirmed by the 

 figures and description of the former, while from Burckhardt's 

 results it may be concluded that the dipnoan brain agrees 

 even more closely in this respect with the amphibian. 

 He shows a dorsal sac divided into a part which is 

 cephalad of the supracommissure, and may be compared with 

 the caudal diverticulum in amia (Fig. 99), and the layer of 

 epithelium cephalad of the diencephal in diemyctylus (Fig. 

 68) ; and a so-called conariiim separated from the above by a 

 velian. His conarium, the Adergeflectknoten of other Ger- 

 man authors — the supraplexus — is a large sac with blood ves- 

 sels around it. The velum, though small, exactly corresponds 

 in position with the diaplexus of diemyctylus, while from its 

 cephalic border are given off the paraplexuses. Whether a 

 true auliplexus exists cannot be determined from his figures, 

 but in its essential relations his conarium seems to be the 

 paraphysis of amphibia. 



This second vesicle of the epiphysis as it is some- 

 times called, is a marked feature of the lamprey's brain, 

 as of the reptile's. Ahlborn (i) shows it in lamprey lying 

 ventrad of the epiphysis or pineal eye. He considers that the 

 cavity of the epiphysis opens into the cavity of the second 

 vesicle ; that the left habena which extends as a white band 

 far beyond the right to the second vesicle, forms the nervous 



