CYTOLOGY OF HYDRACTINIA AND PENNARIA. 213 



CHKOMATIN CHANGES IN THE EGG OF Hydractinia. 



While the cytoplasm is becoming thus transformed, the nucleus 

 has increased in size although it does not become more distinct. 

 The nucleolus is mostly occupied by a large vacuole. In place 

 of the sharply defined chromatin masses in the younger ova, there 

 is a marked change in this particular. The typical chromatin 

 reaction is hardly evident and the whole nucleus tends to take a 

 stain similar to the cytoplasm. The chromatin threads and 

 masses are less definite in position and arrangement. The ques- 

 tion naturally arises, what is becoming of the chromatin ? Can its 

 disappearance be traced into any part of the egg ? In o'her words, 

 is there a definite and specific migration of chromatin from the 

 nucleus into the cytoplasm ? The following facts are submitted 

 in answer to these queries. 



While the eggs are still in the gonophore and the nucleolus is 

 becoming vacuolated, small particles of chromatin leave the nu- 

 cleus and wander out into the cytoplasm. Fig. I, PI. I., shows 

 the early stages of this process, some of the chromatin granules 

 are just emerging. Others have moved some distance. My at- 

 tention was first directed to this phenomenon by finding eggs 

 which showed conditions such as Fig. 2, PI. I., typifies. A num- 

 ber of densely staining chromatin granules are scattered in the 

 cytoplasm and mostly surrounded by a narrow clear area. These 

 masses of chromatin are small and usually single but occasionally 

 two or three are found in a single vacuole. The reason for 

 regarding these masses as chromatin is because they give the same 

 color reaction as similar shaped bodies in the nucleus ; and for 

 the further reason which is obvious in Fig. I, namely, the actual 

 migration of the chromatin from the nucleus. 



o 



When the size of the nucleus of the mature egg, i. e., before 

 maturation, is compared with the female pro-nucleus one is 

 strongly impressed with the great reduction in size. Text-fig. 3 

 is a camera lucida drawing of the outline of the egg nucleus as 

 represented by the larger circle, while the smaller circle within 

 represents the size of the female pro-nucleus. It must be appar- 

 ent at once that up to and during maturation there is a remark- 

 able reduction in the size of the nucleus which the maturation 

 phenomenon alone does not adequately explain. The nucleus 



