EEPEODUCTIVE ELEMENTS IN APUS AND BBANOHIPUS. 281 



that it is not without difficulty that it can be recognised 

 at all. 



Such evidence seems to me to favour the conclusion that 

 the monomeric division in the genital cells of Apus is the 

 most extreme term known in a progressive modification of the 

 more primitive karyokinesis through such forms as Frenzel's 

 " Nucleolare Kernbulbirung/' in which the spindle^ and the 

 breaking up of the chromatin into bands or globes, as well as 

 the resting reticulum, have long since disappeared. 



There seems some probability in the assumption, then^ that 

 owing to the introduction of a peculiar method of reproduc- 

 tion in Apus (parthenogenesis or hermaphroditism), the divi- 

 sional phenomenon has exhibited a corresponding change, that 

 the cells of the genital gland are all alike^ and can function 

 both in slime or egg formation as opportunity arises. 



The egg nuclei take origin from nuclei containing a single 

 chromosome, but they ultimately develop a coarse chromatic 

 reticulum with an external attraction sphere or archoplasm 

 (fig. 42, b), and appear much like an enlarged somatic cell. 



How such a modification of the original type has arisen it 

 is not, perhaps, very difficult to see. In sexually produced 

 species, the nuclei intended for fusion must, so to speak, 

 balance one another; and if karyokinesis is the original method 

 of procedure, any tendency in an individual to infringe this 

 rule in the origin of its reproductive cells would quickly tend 

 to be eradicated from the race on account of the wide abnor- 

 malities it produced. But a parthenogenetic or hermaphrodite 

 species might please itself as to the manner in which it evolved 

 its reproductive elements, so long as these contained the 

 premises necessary to the proper development of the individual. 



