294 FRANZ SCHRADER. 



in several forms. Here may be mentioned Lilium (Weniger, '18), 

 the "goumi aphid" (Stevens, '06), and once more the pronuclei of 

 Psendococcns itself. In the latter case I have mentioned ('23) the 

 possibility that delay in the condensation of chromosomes in one 

 of the two pronuclei may be connected with the peculiar chromo- 

 some conditions of the male. This is at best only a working 

 hypothesis. 



The present account makes it evident that, generally speaking, 

 the fusion of the polar nucleus derivatives with migrating cleavage 

 cells is a more frequent occurrence than I had previously supposed. 

 It therefore seems best to apply the name "polar nucleus deriv- 

 ative" only to the cells carrying 15 chromosomes, which are 

 products of the division of the original, single polar nucleus. In 

 my previous paper ('23) this term was applied somewhat in- 

 discriminately to cells arising from division of the polar nucleus 

 as well to some of those that had already undergone fusion with 

 other cells and therefore contained a multiple number of chro- 

 mosomes. The latter type of cell has been called "giant cell" 

 throughout the present paper and of course includes cells arising 

 from the fusion of polar nucleus derivatives among themselves, 

 as well as with cleavage cells. The distinction between the giant 

 cells and the polar nucleus derivatives is thus made a very definite 

 one. Giant cells that have entered into association with the 



t 



symbionts therewith become mycetocytes. 



No attempt has been made here to discuss the exact relations 

 between the insect body and the symbionts harbored by it. It 

 should be pointed out however that the mycetocytes are insect 

 cells. But they are in a measure extraneous to the organization 

 of the body of the insect and even their actual connections with 

 the latter are confined to branches of the trachea. Even during 

 development they do not stand in a more direct relation to the 

 various organs of the embryo than do the symbionts themselves. 

 Their physiological importance nevertheless may be considerable; 

 but this is a problem in itself. 



I realize that the difficulties of the case are not removed by 

 listing parallel instances of various stages as I have done in this 

 discussion. Such a proceeding however does serve to emphasize 

 that many of the questions brought up by the investigation are 



