EXPERIMENTS IN HYBRIDIZATION AND TEMPERATURE. 13 



highly improbable, and we are therefore limited to the physio- 

 logical aspect. 



The cause of this exceeding difference in fertility of the two 

 above named secondary hybrids must be sought in the different 

 degrees of physiological affinity between the pavonia ? and this 

 hybrid male on the one hand, and between the pi/ri ? and the 

 same hybrid male on the other, as regards the whole physio- 

 gnomical build of this hybrid form. 



The degree of fertility of a form stands now, doubtless, in 

 direct connection with the percentage of gynandromorphic in- 

 dividuals in its offspring ; the greater the fertility the smaller 

 percentage of gynandromorphic forms, and vice versa. 



In this sense the gynandromorphic forms are according to 

 their number entirely dependent upon the species of female used 

 — that is, they are dependent upon the degree of relationship that 

 exists between this female to the parent male. 



We must now come to the conclusion that also the female 

 sexual products possess in poteiitia factors which influence the 

 build of the brood in the sense of normal males and females. 



Now", to go back a bit, to judge the percentage of gynandro- 

 morphism among primary hybrids. This, as we saw, was by no 

 means high, but still higher than among individuals of pure 

 origin. 



The sexual products of both parents are in this case, of 

 course, of normal quality, but not their relationship, their 

 physiological affinity. It seems here actually to be the fact that 

 the less the physiological affinity of the crossed pure species is, 

 the higher the number of gynandromorphic individuals among 

 the resulting hybrids, and vice versa. Among the hybrids of the 

 crossing of S. pavonia <? x pyri ? five gynandromorphic indi- 

 viduals have been noted — three by Mr. W. Caspari (Wiesbaden), 

 and two by me ; whereas among the hybrids of the cross 

 between *S'. pavonia <? x spini ? , to the best of my knowledge, not 

 a single gynandromorphic specimen is known. 



The number of these two hybrids at present bred is about 

 equal, and, from the results of our experiments, it must be con- 

 cluded that the physiological affinity between S. spini and *S'. 

 pavonia is greater than that of S. pyri and pavonia. 



Further, that the degeneration and malformation of the egg- 

 germs which these gynandromorphic forms have been shown by 

 anatomical investigation to possess is directly connected with the 

 appearance of secondary female sexual characters in male in- 

 dividuals, and vice versa. ; the occurrence of secondary male 

 characters in female individuals has long been known to be 

 a fact. 



(To be continued.) 



