96 Journal of Comparative Neurology. 



jority. An investigation of embryos of these forms would be 

 very instructive. 



In the new world monkeys, so far as examined (Hapalidae) 

 there is no absorbtion of the sac, conforming to what was found 

 in the lower mammalia. 



In all these forms, however, the communications between 

 the lateral recesses and the subarachnoid cavity are very large. 



If we attribute a functional importance to these communi- 

 cations in equalizing the intra- and extra-cerebral pressure by 

 permitting the flow of cceliolymph, we can readily see why 

 they should not be necessary in those forms in which a large 

 portion of the walls of the brain are membranous. 



In all forms in which the cerebellum is rudimentary, there 

 is relatively a large expanse of membranous tela in the roof of 

 the fourth ventricle. 



In some of these forms, however, there is a tendency to the 

 formation of a sac-like caudal protrusion of the ventricle. 



If the fresh elasmobranch brain be tilted so that the ccelio- 

 lymph gravitates to the caudal extremity of the ventricle, a 

 bulging in the roof at this point is produced that is quite sug- 

 gestive, although no distinct protrusion is found on sentioning. 

 In the Holostei, Gage has figured a distinct caudal protrusion 

 with recurvation of the lips of the ventricle in Amia. 



In the Dipnoi, Burckhardt has found a similar protrusion 

 in Protopterus, 



In Batrachia through the kindness of Dr. O. S. Strong I 

 have been able to make an examination of the following urodele 

 forms, Amblystoma, Spelerpes, Desmognathus. In them I 

 have found no evidence of a protrusion or metapore. Gage, 

 however, has found an opening in the caudal portion of the 

 roof in the adult Diemyctelus viridescens with the eversion of 

 the lips of the ventricle. 



In the Anura I have sectioned tadpoles of Rana catesbiana 

 and Rana palustris, also adults of the same species and Rana 

 silvatica, and found no ventricular protrusion. In the Reptilia 

 on account of the difficulties experienced in fixation and decal- 

 cification, I have so far been unable to obtain satisfactory sec- 



