358 JOHN WARREN 



cephalic surface of the velum in the lower forms mentioned above 

 really come from the telencephalon if we use the tip of the velum 

 as the boundary between the two regions. However, they lie 

 behind the opening of the paraphj^sis instead of in front of it. 

 Kupffer (57), fig. 227, Triton cristatus, shows the plexus infer- 

 ioris arising behind the paraphysis and forming an unmistakable 

 mass in the lower part of the ventricular cavity. Strictly speaking 

 in spite of the difference in relation to the paraphysis I suppose that 

 the folds on the cephalic surface of the velum correspond to the 

 telencephahc plexus or plexus inferioris of amphibia, while the 

 folds on the caudal surface of the velum would correspond to 

 the diencephalic plexus. In this case there would be in advanced 

 stages practically no line of demarcation between the two plexuses 

 as one could not be sure just what point corresponded to the 

 original apex of the velum. 



The telencephahc plexus reaches its highest development in 

 amphibia forming a very striking median mass in the lower part 

 of the diencephalon. See Necturus, Warren (97), Diemyctylus, 

 Mrs. Gage (32), figs. 6 and 20-22, Ichthyophis, Burckhardt (13). 

 Burckhardt (13) states that it is present in reptiles though in a 

 greatly reduced form. I have found no traces of it in the lizard 

 and have seen no signs of it in the figures of Francotte (28, 29, 

 30), Kupffer (57), Voelzkow (95), or Herrick (38, 39). In the 

 turtle there are two paired masses growing backward from the 

 origin of the lateral plexus into the diencephalon, figs. 22 and 26. 

 These I think may possibly be regarded as homologous to the 

 single median plexus of amphibia. Humphrey (51), fig. 30, found 

 the plexus well developed in Chelydra serpentina, but in birds 

 and mammals it is absent, Burckhardt (13). 



The lateral plexus according to Burckhardt (13) and Edinger 

 (23) «is lacking in teleosts. In Acanthias the lateral plexus is 

 well developed, Kupffer (57), p. 84, and is also seen in Pristiurus, 

 fig. 95. In ganoids it is absent, Burckhardt (13). 



In amphibia it is very well developed and springs from the 

 base of the telencephahc plexus to enter the lateral ventricle, 

 Mrs. Gage (32), fig. 18, Studnicka (93), pi. 7, figs. 8, 13, War- 

 ren (97), figs. 12 and 14. In lizards it appears at 17 mm., fig. 10, 



