Spermatogenesis in spiders. 569 



crossing- population the females would ultimately become of three 

 kinds, namely : a) females which carry two measures of the ctetosomes, 

 b) females which carry one measure of the ctetosomes and c) females 

 which carry no ctetosomes at all, the determination of the character 

 in the males would not vary from the simple scheme given. 



One further fact which tends to give strength to the assumption 

 that the planosomes play no part in heredity, is found in one gray 

 male, which shows the presence of a small nucleolus in the growth 

 period (Fig. 30). For a long time the presence of this body was 

 not understood but the explanation is apparently very simple. If 

 we will examine Diagram IV, it will be seen that the planosome may 

 be carried by the female producing sperm or the male producing 

 sperm. There is no reason why such a male producing sperm might 

 not fertilize an e^g which carried the ctetosomes, thus producing 

 a gray male which carries the planosome. Evidently, this is what 

 we have in the one case. 



It should be pointed out further, that in the case of Amaurobius 

 sylvestris, all the males examined carried the ctetosomes and these 

 are equally distributed during the last sperm atogonial division, 

 apparently. Since the males are all alike, it seems probable that 

 the eggs will be of one kind, as regards these bodies, and even 

 though the ctetosomes of this form might play some part in heredity, 

 we should not be able to see it. 



It is of interest to note, that if the presence or absence of the 

 ctetosomes determines the dimorphism of these males, and if the 

 ctetosomes come from the Y-element, as seems most probable at the 

 present time, then the dimorphism first appeared when the X-and 

 Y-elements failed to separate in the first maturation division, sometime 

 in the history of the species. 



