8 J. T. PATTEESON 



that it came from the oocytic nucleus, and hence its name. This 

 structure has given rise to a great deal of discussion, and no 

 less than five different theories have been advanced to explain 

 its genesis. It was not observed by Marchal ('04) for the egg 

 of Ageniaspis, but later Silvestri ('08) and Martin ('14) both 

 demonstrated its presence in the egg of this species. Martin, 

 who gives a very clear account of the history of this body, first 

 demonstrated that it arises outside of the germinal vesicle before 

 the nuclear wall breaks down, and hence could not be regarded 

 as a true nucleolus. He showed that it first appears in a 

 young oocyte as a collection of small deeply staining bodies, 

 among a cloud of very fine granules, situated near the posterior 

 end of the cell. It gradually increases in size and becomes fully 

 formed at about the same time the egg attains its full size. 



In the meantime, Hegner ('14) also showed that in the egg of 

 Copidosoma gelechiae the nucleolus was not a plasmosome 

 coming from the germinal vesicle. However, he reached the 

 untenable conclusion, based on a study of an incomplete series 

 of sections, that the matured egg was a composite structure, 

 produced by the fusion of two oocytes. He thus derived the 

 nucleus of the egg from the germinal vesicle of one of the oocytes 

 and the nucleolus from that of the other oocyte. 



Silvestri ('14) replied almost immediately in an article deal- 

 ing with the development of Copidosoma buyssoni. In this 

 paper he admits his error in deriving the nucleolus from the 

 germinal vesicle of the oocyte, and suggests the possibility that 

 it may arise from a group of granules lying near the posterior 

 side of the nucleus. He offers the term oosoma in lieu of nucle- 

 olus. He also points out that what Hegner regarded as a 

 composite structure in sections is in reahty only the anterior 

 and posterior ends of the same oocyte — a correction which 

 Hegner ('15) accepts. 



The chief interest in the nucleolus lies in the fact that a very 

 important function has been assigned to it by Silvestri and 

 Hegner. Silvestri ('06) showed that it is distributed to a single 

 blastomere of the four-celled stage in Litomastix, and suggested 

 that this cell may be the progenitor of all the germ cells of the 



