110 bulletin: museum of comparative zoology. 



In the case of unequal tetrads, however, variation in shape does 

 have some meaning with reference to chromosomal organization. In 

 the specimens of Phrynotettix which I have studied, the shape of 

 tetrad B in two individuals is fundamentally different from that in 

 the other eleven, because, in the latter, a definite part of one member 

 of the pair is lacking. Similarly, in the case of Ci and C2, the difference 

 concerns a definite part of the members of the pairs. But the im- 

 portant thing to be kept in mind is that the organization of each of 

 these tetrads is constant for any individual animal, and such differ- 

 ences as exist between individuals can be readily accounted for. 



b. Persistent Organization of Chromosomes. 



1. The selected chromosomes. — One of the most important con- 

 clusions arrived at in the present study relates to the constancy in 

 the finer organization of the chromosomes, both from stage to stage 

 in the same individual, and from one individual to another. This 

 is shown in two ways : — first, by the existence in chromosome-pair 

 B of an architecture that is constant both for any one individual in 

 the various stages in which any architectural condition could be 

 recognized, and likewise for all the individuals studied; secondly, by 

 that of a particular pair of chromosomes (A) recognizable through all 

 the stages from spermatogonia to spermatids, the recognition being 

 made possible by the fact that the chromosomes in question possess 

 properties which are characteristic and constant for all stages. 



Both of these selected ^chromosomes, A and B, tend to stain more 

 deeply than the other autosomes, but this tendency is much more 

 marked in A than in B. If chromosomes possessing similar peculiari- 

 ties be found in related species, may they not be regarded as homolo- 

 gous to the selected chromosomes A and B of Phrynotettix? I think 

 such homologies could be established. Miss Carothers ('13) shows 

 that the small unequal tetrad in Brachystola is usually associated 

 with the accessory chromosome, and is more intensely stained than 

 the other autosomes. Might it not be possible to analyse this un- 

 equal element in Brachystola and determine its relation to the unequal 

 tetrads of Phrynotettix? Since these two genera are closely related, 

 I believe this would be possible. Furthermore, the other unequal 

 tetrads described by Miss Carothers for Arphia and Dissosteira were 

 among the small chromosomes and, on account of the similarity in 

 behavior, might be found homologous to 5 or C of Phrynotettix. 



