." , 



I'l - . .1110 important drviati >ns fnm t ln pm-vss of tliv: 



jti>t dr.-i-rihod, \\ hie li atle.-t t hi- form of t he ! WBgt pr. dud , ftll : 

 l'a\ing unaltered the tiiicr prOOeflSeS M-lrttini: to tin- nucleii-. The 

 de\ iations aie induced, OS \\6 shall :-how more in detail in the in 

 dividual ea>e>, by tin- variation in t he amount of drut>pla>m emit ained 

 in tin- eggS, and l>y tin- pie\ i<>u-ly desci il>"d varial>ility in its di-tribu- 

 tit. n. One may appropriately separate the various torm- ct tin* 

 prOOeeB >f i-lea/airr into two ( -l.-i-x-s. and cadi rla>s into t\\o >uh 

 <-laf>. although tin- forms merge into one another by m-a: 

 transitional condition.-. 



To tin- !ir>t c-la.-s \\e as>i_i:n >i;ch 



into x,,jinent8 by the process of cleavage. The cli-axau'' 1 it>elf we 

 as total; and according as t he Moments are <f e.jual or un- 

 -i/.\ we distinguish as .siihdivisinns ^jmd cleavage and wwqtuU 

 rlea\ 



With total is contracted ^n-t'ml oUavagA This occurs in the 

 \vhii-h ai-e provided with \ ery ahnndant deutoplasin, 

 and are consequently of considerable six-.-, and in which, at the E 

 timo, the previously described separation into formative yolk and 

 nutritive yolk has boon distinctly e>t ahlishcd. In this case th< 

 mative yolk alone undergoes a process of cleavage, whereas the chief 

 ma>s of the egg, the nutritive yolk, remains undivided, and in general 

 unatleeted, hy the processes of embryonic development; hence the 

 name partial cl>'>tv(t</e. This, in turn, is resolvable into tho two >uh- 

 types of discoidal and .v///:/v/oV fAw/v///.-, accordini: as the forma- 

 tive yolk rests as a disc upon the nutritive yolk, or envelops tin- 

 latter as a thick cortical layer. REMAK has designated eggs with 

 total segmentation as kolobhutic, those with partial s?gmi-i.' 



\\'e may therefore present the following scheme >f cleavage: 



i. TYW 



Total cleavage : \ 



(a) Equal cleavage HoU>i>l;istic cgga, 



(i) Unequal cleavage J 

 II. TYI-K 



Partial cleavage: \ 



(n) l>ix'oi<lal rlravage M-Tol -hustle eggs. 



(/>) Superficial cleavage J 



I a - Equal Cleavage. 



In the general consideration of tie process of cleavage we have 

 already become acquainted with the phenomena of equal >egmenta- 



