8o Journal of Comparative Neurology. 



neurites to the hypothalamus and gangHon habenulae as in 

 other fishes. 



35. The nucleus thaeniae sends its neurites to the same 

 destinations. 



36. There is no cortex. 



37. The olfactory lobe has a large number of slighly dif- 

 ferentiated cells which receive and transmit olfactory impulses. 

 The mitral cells are few in number and very poorly developed. 



38. The brain shows marked primitive characters in cer- 

 tain centers and especially in the morphology and disposition 

 of its individual nerve elements. 



39. This brain offers considerable evidence that brain cells 

 are primitively epithelial in character and that they increase 

 their complexity of form and their functional efficiency as they 

 become removed from the central cavity (or the external 

 surface). 



40. The conditions in Petromyzon suggest that the prim- 

 itive vertebrate brain had a complete choroid roof for its whole 

 length, thickened only by commissures. 



Morgantown, IV. Va. 

 October 16, igoi. 



List of Papers Cited. 



(For additional papers see the list in '01 c). 



Ahlborn, F. 



'83. Untersuchungen iiber das Gehirn der Petromyzonten. Zeit. f. wiss. 



ZooL, Bd. 39, p. 191-294. 

 '84. Ueber den Ursprung und Austritt der Hirnnerven von Petromyzon. 

 Zeit. /. 7uiss. ZooL, Bd. 40, p. 238-308. 

 Alcock, R. 



'98. The peripheral Distribution of the Cranial Nerves of Ammocoetes. 

 /our. of Anat. and Physiol., Vol. t,2)^ ^^- i- 

 Cole, Frank J. 



'98 a. Observations on the Structure and Morphology of the Cranial 

 Nerves and Lateral Sense Organs of Fishes ; with especial reference 

 to the genus Gadus. Trans. Linn. Soc. London, Vol. 7, No. 5. 

 '98 b. The peripheral Distribution of the Cranial Nerves of Ammocoetes. 

 Anat. Anz., Bd. 15, No. 11-12, p. 195-200. 



