358 EYCLESHYMER. [Vol. X. 



In the eggs of Merlucius, studied by Kingsley and Conn ('83), 

 " the blastomeres varied widely in size, and the segmentation 

 furrows progressed at varying rates in different portions of the 

 germinal areas." Agassiz and Whitman ("84), Henneguy ('88), 

 and others have observed like differences in the size of the 

 blastomeres of the second cleavage. I have never found the 

 second furrows passing in a horizontal plane, yet Kupffer ('68) 

 found this to be the case in the Herring, and List ('8?) ob- 

 served the same in Crenilabrus. 



The condition represented in Fig. 27, presumably derived 

 from a form like that shown in Fig. 23, is of rare occurrence. 



The form depicted in Fig. 28 is one likewise seldom ob- 

 served, and it may be said that in the White-fish the typical 

 six-cell stage of other Teleosts is only one of the many varia- 

 tions. 



The meridional nature of the third cleavage in Teleosts is 

 generally agreed upon, with the exception of Brook ('86) who 

 holds that it is equatorial. 



In the eight-cell stage, if such it may be considered, the 

 cells show endless variations in arrangement, the bilaterally 

 symmetrical form shown in Fig. 33 being very seldom found, 

 that indicated in Fig. 32 more often, and most frequently 

 some variation of that observed in Fig. 30. A radial arrange- 

 ment about a central cell (Fig. 29) is occasionally observed. 



While the majority of investigators have considered the 

 cleavage of the Teleost-ovum as fairly regular, we find the 

 cleavage of Coregonus quite the opposite; we may also infer 

 from the work of Rauber ('83) that in certain forms if any two 

 blastoderms, in late cleavage, were superimposed the furrows 

 would nowhere coincide. Ryder also states " that it is proba- 

 bly true that most eggs will be found to vary more or less 

 notably." 



The forms shown in Figs. 30, 31, and 32 are probably the 

 derivatives of an unequal two-cell stage. The wide separation 

 of these groups of cells is a point of interest. A like condi- 

 tion has been figured by Miss Clapp ('91) in the eight-cell 

 stage of the Toad-fish, but nothing is said concerning its 

 significance. 



