140 



THE AMEBIC AX NATURALIST 



[Vol. LIII 



ground. This matter can be, and is being, investigated.) 

 On the other hand, it as often happens that when an in- 

 dividual reproducing parthenogenetically is mated she 

 thenceforth gives offspring all showing male parentage. 

 Also, though less readily, a mated female reproducing 

 exclusively bisexually, when placed to herself, will, after 

 a few weeks, give offspring parthenogenetically. Al- 

 though the end result data which might give light on this 

 point have not as yet been adequately developed, I ven- 

 ture the suggestion that with respect to the need of fer- 

 tilization the mature eggs are approximately the same, 

 and that it is the time of the entrance of the sperma- 

 tozoon which determines the matter. If a spermatozoon 

 enters the egg at the proper stage of its maturation the 

 pronuclei unite; if no spermatozoon enters, or one enters 

 too late, the egg either proceeds parthenogenetically, or 

 fails to develop altogether. 



The diploid number of chromosomes in the Apofeftix 

 female appears to be fourteen. This number has been 

 clearly demonstrated in the late metaphase plate of an 

 oogonial division in an individual derived bisexually. In 

 a preparation of soniatic c -lis of n female produced par- 

 thenogenetically, iiiiii' appar(>iitl\- Avhole chromosomes 

 and some f rauiiiciits were ol)st'Vved in one (Mr. A. H. 

 Hersh, unpublished.) The females of some other mem- 

 bers of the Te1tiui(l;e ha\(^ fourteen chromosomes (Rob- 

 ertson, '16). Ill some forms of the Tettigida^ the males 

 have been shown to have thirteen chromosomes as the 

 complete number (Harman, '15, and Robertson, '16). 



The ''maneuvers of the chromosomes" theory of Mor- 

 gan may very well account for the observed end results 

 presented in this paper, though the possibility of some 

 other explanation is not by any means excluded. Even 

 if the results herein entitled "crossing-over" should at 

 some time be found aetnally not to be connected with 

 the maneuvers of tin- chrotiK.sonies. the i<'ini mi,i;ii1 still 

 be retained as an adeijnnte expi-.-ssion of \vhate\cr does 

 occur. The discussion of the mechanism, physiological 



