145 



imprassioris r-idiat.e:! from the adjacent olfactory nuclei; it 

 therefore anticipates the olfactory connections of the reptil- 

 ian ani higher brains. Tne tractas pallii, arising from the 

 pallial neurones, is regariei as giving the olfactory sense a 

 quite direct connection with posterior regions. 



2. Conclusion. 

 To one fho has read this far, it must be evident that 

 thera is a most remarkable structural similarity bet^esn the 

 brain of Mustelus and the brains of higher vertebrates. The 

 results obtained by me do not bear out the conclusions of 

 Szczawinska ('98) relative to the very low plane occupied by 

 the selachian neurones; see Section II, 2. The neurones of 

 Mustelus are, of course, simpler in their external morphology, 

 and their architect jral relations are of a far less complicated 

 order, yet it is none the less true that they anticipate the 

 conditions found in higher vertebrates in all important partic- 

 ulars. Such a fact is certainly the more remarkable when the 

 great differences in the scale of general organology are taken 

 into account. The fact can only be interpreted to mean that 

 the nervous system of the primitive vertebrate had its essen- 

 tials of organization veil defined before the divergence of the 

 several phyla occurred. A brain of the type presented by the 

 selachian of to-day has not become sufficiently specialized du- 

 ring the lapse of time entirely to mask the ancestral charac- 



