140 CYTOLOGY 



CHAP. 



of the chromosomes of the type form, each hmb corresponding to a 

 whole rod-shaped chromosome, thus accounting for the usual 23 chromo- 

 somes by II simple +6 double elements. 



This association has of course not taken place between homologous 

 chromosomes, but between non-homologous ones. Thus, using the 

 notation on p. 124, Unkage has occurred between each A and B, C and D, 

 E and F, etc., to form composite chromosomes of the formula AB, CD, 

 EF, etc. This interpretation is borne out by the facts that the six V's 

 form three equal pairs, and also that the hmbs of each V are not equal, 

 showing that the linkage has been between non-homologous chromosomes. 



M'Clung (1917) has come to similar conclusions regarding the variation 

 in the number of chromosomes in Hesperotettix viridis, one of the Acridiidae. 

 In this species the type nimiber for the femiily (23 in the male) is found 

 in some individuals, but others exhibit fewer. An examination of the 

 bivalents of the primary spermatocytes shows that in the latter individuals 

 one or more of the chromosomes have a transverse constriction which 

 is not found in those individuals which possess the full 23 chromosomes, 

 probably indicating that the chromosomes in question are compound. 



Thus, in their primary spermatocytes — 



5 individuals had 12 separate chromosomes = 1 1 bipartite + the sex chromosomes. 



II ,. =10 bipartite + i tripartite (the sex 



chromosome attached to one 

 ordinary bivalent). 



= 8 bipartite + i quadripartite + i tri- 

 partite. 



= 6 bipartite -|- 2 quadripartite + i tri- 

 partite. 



= 7 bipartite -r 2 quadripartite + the sex 

 chromosome. 



= 9 bipartite -|- 1 quadripartite + the sex 

 chromosome. 



5 .. 10 

 7 .. 9 

 7 .. 10 



6 .. II 



It will be seen that the number of chromatin segments in all cases 

 adds up to 23, the bipartite chromosomes being of course the ordinary 

 bivalents formed by the pairing of two simple homologous chromosomes, 

 the quadripartite ones being formed by a pair of composite homologous 

 chromosomes (each of which has been formed by the Knkage of two 

 non-homologous chromosomes as in Chorthippus), and the tripartite 

 forms by the junction of the single sex chromosome with an ordinary 

 bivalent. The condition presented by the first example in the table is 

 the typical one for the family when there is no linkage of chromosomes. 



Again, all the nuclei of a given individual have the same type of 

 chromosome complex. What happens in fertilization between different 

 classes of individuals is not known. M'Clung suggests that the Unkage is 

 resolved, and re-formed, at syngamy. 



Woolsey (1915) found similar relations in the locustid genus Jamaicana 



