CHAPTER IX. 



KOTATOKIA. 



The Rotatoria are peculiar in regard to their reproduction. 

 Three different kinds of eggs occur among them : in the 

 first place, thin-shelled summer eggs, which develop par- 

 thenogeneticallj into females ; then eggs similar to these, 

 but of only half the size, from which arise the simply 

 organized males ; and finally thick-shelled winter eggs or 

 resting eggs, which, as it appears, require to be fertilized. 

 The eggs are either deposited free in the water or cemented 

 to the body of the female. The development of the thin- 

 shelled eggs takes place in many forms even in the body 

 of the mother ; that of the resting eggs occurs only a loner 

 time after laying. 



The expulsion of the polar globules precedes cleavage. 

 The parthenogenetically developing eggs, according to 

 Weismann und Ischikawa, produce only one polar globule. 

 Little is yet known concerning the development of the 

 Rotatoria. The chief descriptions are from Salensky, Joliet, 

 and Tessin ; they present, however, many gaps. In our 

 presentation of the subject we follow principally Tesrin's 

 work, which is occupied chiefly with the development of 

 iJosphora digitata. 



Cleavage is fi'om the beginning unequal (Tessin, Joliet). 

 In the stage of four blastomeres one large and three small 

 cells can be distinguished (Fig. 115 A). At the time when 

 the latter divide into six, the abstriction of a new portion 

 from the large blastomere takes place, and when those cells 

 which subsequently supply the mesoderm are differentiated 

 from the cells at first produced, a division of the large 

 blastomere is still in progress (Fig. 115 J5). That part of 

 it which is now left as a rather extensive remnant represents 



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