CYTOLOGY OF HYDRACTINIA AND PENNAKIA. 22Q 



the cytoplasm never to return to the nucleus so far as one can 

 determine ? This certainly seems to be a kind of fragmentation. 

 Why does it occur? Has the maturation phenomena failed to 

 fully prepare the egg nucleus for fertilization ? These are ques- 

 tions which those who would make the development of all eggs 

 conform to a definite series of changes must explain. 



Amitosis. By this process it is understood that the nucleus 

 divides without the chromatin passing through a complicated 

 series of changes and without the formation of a spindle. Fre- 

 quent search has been made for amitosis in these eggs but with- 

 out finding any positive evidence. The irregular and claviculate 

 shaped nuclei were critically observed and in every instance 

 eventually either asters or the very characteristic chromatin 

 changes were taking place in them. The mere shape of the 

 nucleus in Pennaria is no indication of amitosis, nor is it neces- 

 sary that the chromosome vesicles become transformed into the 

 single "resting nucleus." The cluster of vesicles which Hargitt 

 frequently finds is not uncommon in my material but is interpreted 

 in tliis paper as late telopJiase. This is a point concerning which 

 there may be a difference of opinion but taking all of the facts 

 into consideration, these vesicles seem to me to indicate mitosis 

 rather than amitosis. 



INCLUSIONS IN Pennaria. 



There are found in the eggs of Pennaria, even before matura- 

 tion, bodies which for the lack of a better term are designated 

 inclusions, Fig. 29, PI. IV. Thus far they have not been seen in 

 the segmenting egg. As many as three such inclusions have 

 been discovered in a single egg. When newly formed, the sub- 

 stance of the inclusion takes the same stain as the surrounding 

 cytoplasm, but in the older stages this contained substance stains 

 faintly, eventually leaving a cavity. This cavity then is obliter- 

 ated by the encroachment of the cytoplasm. The substance 

 within the inclusions in appearance and staining reactions is cer- 

 tainly similar, if not identical, to the cytoplasm, and the whole 

 structure looks like a food-vacuole in which cytoplasm is being 

 digested. Their origin has not been determined. They can 

 hardly be regarded as polar bodies, because they may appear 

 before maturation begins. 



