634 Theophimts S. Painter, 



males. ^) There are two possible interpretations, the one being that 

 the tiifted male has arisen through sexual selection, the Interpretation 

 taken by the Peckhams, and the other is that this later form has 

 arisen as a mutation. 



It seems worth while to bring- up the subject here, as there are 

 certain observations which, it seems to me, totally eliminates the 

 origin of the tufted males by sexual selection. It has often been 

 observed in the laboratory, both by Professor Peteunkevitch and 

 by myself, that the females do not seem to show any preference 

 for the tufted males and the same female has been observed to 

 copulate with a tufted and a gray male within a period of five 

 minutes. Futhermore, the species is very widely distributed throughout 

 the United States. The Peckhams (1909), remark: "This is a very 

 common species. Mr. Banks has found it in Colorado, Mr. Emerton 

 in Massachusetts and Connecticut, and we have it from Georgia, 

 Missouri, Wisconsin, Nebraska and Kansas" (p. 453). 



It seems that if sexual selection were at work here, that it has 

 had sufficient time to make the gray males very rare. As has been 

 shown, they are equally as numerous as the tufted males. It might 

 be mentioned here that the tufts do not seem to play any part in 

 the mating of this variety with the females, Two of my matings 

 have been made with tufted males, one of which had lost all three 

 tufts, and the other specimen only had the right one left. 



The other alternative, that this later form has arisen through 

 a sudden discontinuous Variation, seems the more satisfactory. The 

 Author has suggested the cause of this dimorphism from a cyto- 

 logical study. It was found that the gray males carried a pair of 

 small chromosomes, called "ctetosomes" because of their behavior, 

 while the tufted males lacked these bodies. Furthermore, from a 

 comparative study with species of twelve other families of spiders, 

 it seemed probable that these ctetosomes were to be derived from 

 a Y-chromosome, the primitive Arachnida having the XY condition 

 in the male sex and the XX condition in the female. It was sug- 

 gested that when the Y-chromosome became associated with the X 

 or accessory chromosome, a condition we seem to have at the present 



1) The reason for this, is, that among Jumping spiders, generally, 

 the males are very much like the females before the latter have becorae 

 mature. That the gray males of Maevia vittata are like the immature 

 females, has been known for a long time and it would show that the 

 former was an older type than the tufted male. 



