SEGREGATION OF HOMOLOGOUS CHROMOSOMES 469 



correlated with the reduction (Circotettix and the Stenobothrus- 

 like form described by McClung, '14). Yet structurally one is 

 an octad the other a tetrad. The octad has true terminal spindle 

 fiber attachment, so far as the tetrads composing it are concerned, 

 while the ring of the other type has real nonterminal spindle 

 fiber attachment. 



g. Supernumeraries. Another variation which has attracted 

 attention in our collection of Acrididian material for the first 

 time and which is relatively very abundant in the specimens 

 collected during the summer of 1915, is the presence in certain 

 individuals of one, or sometimes two, entities which I shall 

 designate as supernumeraries. They possess the staining ca- 

 pacity of chromatin. In the spermatogonia they enter the 

 spindle at metaphase and divide like any chromosome (fig. 62a, 

 chromosome s, plate 11 shows this body in the spermatogonia). 

 In the plates of the first spermatocytes these bodies have been 

 placed to the left of chromosome number 12, and a glance 

 through plates 2 to 10 will show their frequency of occurrence. 

 Individual number 10 (plate 2) of form 'A' possessed two super- 

 numerary chromosomes, one more than twice the size of the other. 

 This was the only animal in this group which possessed super- 

 numeraries. But when we pass to form 'B' (plates 6-9) we find 

 them in eight out of thirty-one individuals, that is, in more than 

 one-fourth of all the animals studied. 



I would especially call attention to the similarity between the 

 supernumerary and accessory in specimen number 62. 



The suprenumeraries are also present in two of the eleven 

 Circotettix studied. It is evident from the plates that these 

 elements vary greatly in size; when two are present in a given 

 individual there may be very little resemblance between them. 

 At the first spermatocyte division they pass to one pole undivided. 

 When two are present they segregate freely in relation to the ac- 

 cessory and to each other. At the second spermatocyte division 

 they again enter the spindle, at least usually, and divide as in 

 the spermatogonia (plate 13, 62e). 



