seen that in the two globules of division which have the 

 longitudinal form, one nucleus is biscuit-shaped, and the 

 other consists of two isolated parts. After that, when the 

 nuclei become elongated (in slugs this is seen also in the 

 intact globules of division] , each yolk globule stretches 

 and becomes pear-shaped. Then the twisting occurs in this 

 form so that the newly forming globules are of unequal size, 

 each separating a region of one third the size. The four 

 smaller globules become displaced and are situated in the 

 spaces between the larger two (Figure 39, 40) . "The remarkable 

 reciprocal situation of the yolk globules," Warnek wrote, 

 "is kept and is repeated in all the following stages; this 

 allows one, without ever noticing the further formation of 

 the yolk globules, to solve the question, what globules of 

 division result from each present globule. During this it 

 is necessary to keep in mind the position of the nuclei and 

 the relative size of the yolk globules" (p. 153). 



These accurate observations surpassed those investiga- 

 tions of nearly a quarter of a century afterwards. By the 

 initiative of A. 0. Kovalevsky, the blastomeres of the 

 dividing ova were given individual designations (in letters 

 and numbers) , tracing during the process of development the 

 fate of each blastomere and its derivatives. Warnek formally 

 applied a less suitable and obvious method of designation 

 of the globules of division and their descendants. He 

 named the blastomeres arising in one or the other stage by 

 the number of this stage, keeping for them the same designa- 

 tion also in the following stages of division. During this he 

 mentioned that the yolk globules changed from stage to stage, 

 so that, for example, during the transfer to the fifth stage 

 the globules of the fourth stage were already unequal to the 

 globules of the fourth stage at the moment of their formation. 

 They decrease in size and are changed by chemical properties 

 and internal structure. 



THE FIFTH STAGE. In this stage the formation of 

 the new globules of division follows the rules which also 

 hold for the following stages of division. Instead of the 

 sixteen yolk globules which must be present if each of the 

 eight globules of the fourth stage is divided, here only 

 twelve globules are found. This can be explained by the fact 

 that during the fourth stage only four large globules are 



553 



