No. 5S4] 



BILA TEEALIT Y IN VERTEBRATES 



511 



cells, and on the darker side of the upper hemisphere. If this be the 

 sperm track it does not determine the median plane of the embryo. 



It is thus obvious that the findings by Professor Whit- 

 man not only lend confirmation to my observations on 

 ^laterality, but that they in reality anticipate them. 



It may be said with added confidence that bilaterality 

 in the vertebrate egg is revealed through the early cleav- 

 age grooves. The cephalic portion of the embryo is in- 

 dicated by the area in which cleavage grooves first appear 

 and in which cellular division is most rapid. The caudal 



each other constituting an embryonic tract. 



In addition to the above observations, Professor Whit- 

 man's manuscript and drawings give the results of a 

 series of puncture experiments in the blastoporic lip. 

 Since these observations have an important bearing on 

 the question of epiboly, emboly and concrescence, they 

 are appended. 



