144 



General summary. 

 From the above considerations it seems probable that the total 

 number of primitive encephalomeres was eleven, divided as follows: 

 Fore-brain 3. 

 Mid-brain 2. 

 Hind-brain (i or 5. 



The following points I think are fairly well established in the em- 

 bryos of Godus morrhua. 



1. The neuromeres appear at a late period in the ontogeny and 

 soon degenerate, thus disproving the supposition of their mechanical 

 formation and strengthening that of their phylogenetic importance. 



2. The olfactory pits develop early in connection with the I. pair 

 of nerves, which arise from the fore-brain and seem to have no con- 

 nection with the Prosencephalon , there being no trace of an olfac- 

 tory lobe. 



3. The fore-brain contains three neuromeres. From the first, 

 the roots of the olfactory nerves arise : at a point somewhat above the 

 second the optic diverticula are formed ; from the third no nerve seems 

 to arise. 



4. The mid- brain is composed of two well marked neuromeres 

 slightly smaller and more semicircular than those of the fore-brain. 



5. The hind-brain neuromeres of the Cod correspond h\ number 

 and character to those described by Orr and McClure for that region 

 in the Amphibia and Sauropsida. In Ambly stoma but five are to be 

 seen, as these authors have pointed out. 



The following were less definitely observed. 



6. Evidence of the origin of the III. and IV. nerves from the two 

 neuromeres of the mid-brain is unsatisfactory. The first one in the Cod 

 seems to give origin to some fibres which may correspond to the III., and 

 from the second, in Amblystoma, at a high level . some cells are proli- 

 ferated which may represent the IV. 



7 . There seems to be no doubt as to the origin of the hind-brain 

 nerves as described by Orr and McClure. I think however I am 

 able to confirm Orr's statement Avhich McClure considered doubtful, 

 viz. that the VI. nerve arises from the ventral portion of the second neu- 

 romere , at least in all forms in which six neuromeres are present in 

 the hind-brain. 



Princeton, March 10, 1891. 



