DEVELOPMENT OF PARACOPIDOSOMOPSIS 7 



The chromosomes then become shorter and thicker, and appear 

 to unite near their ends — a process somewhat resembhng sjaiap- 

 sis. The pairs of chromosomes straighten out and become ar- 

 ranged m a parallel series, with the points of union lying at the 

 equator. According to Hegner, the number of rods thus arranged 

 is eleven or twelve, but in realitj^ there should be only ten, for 

 the cytological studies of two of my students have demonstrated 

 clearly that the diploid number of chromosomes in Copidosoma 

 gelechiae is twenty. At first the parallel pairs of chromosomes 

 are scattered, but the entire mitotic figure soon undergoes con- 

 densation, by which the chromosomes become shorter and thicker 

 and are brought close together. Finally, there is produced a 

 homogeneous mass of chromatin, and all trace of individual 

 rods is lost. 



Martin's account of the origin of the nucleus in Ageniaspis, 

 although differing in details, is m agreement with that just 

 given for Copidosoma. The entire process is peculiar, especially 

 in the light of the maturation divisions, which are soon to be 

 described. It may be, as Hegner ('14) suggests, that this pre- 

 cocious, mitotic-hke figure is comparable to the disappearing or 

 aborting spindle which has been observed in the eggs of tur- 

 bellarians and polyclads. The important point is that the 

 chromatin body foimd at the anterior end of the freshly laid 

 egg of these parasites is a derivative of the germinal vesicle, 

 and hence is the true oocytic nucleus. 



In fertilization the entire spermatozoon enters the egg. The 

 head of the sperm is frequently sickle-shaped, with a long taper- 

 ing tail attached (figs. 1, 3). Apparently, the sperm may enter 

 the egg at any point on the surface of the posterior region. This 

 conclusion is based on a study of many fertilized eggs which 

 had just been deposited. Both JMarchal ('04) and ^Martin 

 ('14) believe that they can demonstrate the presence of a micro- 

 pyle on the surface of the anterior process of the egg of Ageni- 

 aspis, which would indicate that the entrance of the sperm was 

 restricted to that point. 



The most remarkable body present in the cytoplasm is the so- 

 called nucleolus. It was first described by Silvestri, who thought 



