30 DUBLIN 



in the first polar body formation, a cap of pure cytoplasm 

 appears at the periphery (Fig. lOi) and into this the peripheral 

 chromosomes move to form the second polar body. 



In the meanwhile, the first polar body has divided. This, in 

 Pedicellina, as in most other forms, TJialasscma (Griffin), Lhnax 

 (Mark), etc., is a very common occurrence and is accomplished 

 by mitosis (Fig. 1 102), The chromosomes, of the same size and 

 form as those observed in the second maturation division, are so 

 placed in the spindle, that they are divided longitudinally like 

 the other bivalents in the ^g^. In the metaphase, a deep con- 

 striction occurs on both sides of the polar body which leads to 

 complete division. From the many cases of second maturation 

 spindles observed, it appears that the division of the first polar 

 body is accomplished very early ; indeed, is completed by the 

 time the second maturation division within the ^gg has reached 

 its metaphase. 



A brief account of the cytoplasmic changes of the growing 

 Ggg" "^ay be appended. In the very youngest oocytes, after the 

 synaptic phase, the cytoplasm is but barely visible as a thin 

 layer around the newly reconstructed nuclear membrane. 

 This rapidly increases, especially at the pole opposite that of 

 chromatin concentration. Thus arises a cytoplasmic polarity 

 characteristic of the oocyte during the whole growth period. 

 The structure of the cytoplasm of the sublimate fixed material 

 appears as a mesh-work of fine microsomes or granules which 

 are imbedded in a continuous substratum. Later, a new ele- 

 ment makes its appearance in the form of large yolk granules 

 which arise at first on the periphery of the cell as deeply stain- 

 ing spheres of various sizes, and increase in numbers by the for- 

 mation of successive layers inward toward the nucleus. I am 

 unable to decide whether the yolk masses arise in situ or actually 

 move inward from the periphery where they are formed. 



Of the considerable number of oocytes which begin their de- 

 velopment, only a portion reach maturity ; the remainder are 

 converted into nutritive cells. These may be distinguished very 

 early. Within the nucleus constant and distinct differences may 

 be observed. The chromatin is not in the form of distinct chro- 



