NUCLEOLI IN PEDICELLINA AMERICANA. 355 



within the nucleus. By this it is not meant that the chromosomes 

 lose their individuality or fuse into one indiscriminate mass. On 

 the contrary, in most forms examined on this matter and in 

 Pedicellina particularly, the persistence of this individuality is most 

 marked although it is impossible to distinguish between the pater- 

 nal and maternal chromosomes now mingled among themselves. 



This conclusion is not only more in accordance with the facts 

 but can alone directly explain the possibility of a parental synapsis, 

 i, e., the union of the homologous paternal and maternal chromo- 

 somes into pairs, thus reducing the number to one half at the 

 close of the oogonic and spermatogonic cycles in the early germ- 

 cells (Montgomery and Sutton). Were the homologous chromo- 

 somes segregated at this period also, this union would be 

 impossible ; mingled together, however, as Moenkhaus has actu- 

 ally shown in the teleost and as is very probable in other forms, 

 the union would be readily effected. 



What then is the significance of the two nucleoli so constant 

 in the life history of Pedicellina / In the present state of our 

 knowledge, when such uncertainty as to the nature and function 

 of the nucleolus still persists, no definite answer can be given. 

 In Pedicellina it is clear that they are not chromatin bodies and 

 come only incidentally into connection with the chromosomes. 

 They are plastin bodies in some way, very probably, connected 

 with the waste products of division, as Hacker's theory main- 

 tains. Yet, whatever may be the significance of the nucleoli as 

 organs of the cell, they do in some way reflect or represent the 

 activities of the nuclear areas in which they arise. When, there- 

 fore, we find in the cells of the cleavage and later stages two 

 nucleoli removed to opposite portions of the nucleus we may 

 perhaps be permitted to infer that these are the outward expres- 

 sions of the activities of these two portions which together com- 

 pose the nucleus, and if an interpretation of parental nuclear 

 autonomy be at all justified by the facts, and this is very ques- 

 tionable, I should suggest that it is much more probable that 

 this autonomy applies to the paternal and maternal sap or ground 

 substance in which the chromosomes are distributed. 



In this connection, there is one more consideration to which 

 attention must be drawn. In the spermatid of Pedicellina, the 



