536 CLARENCE E. McCLUNG 



V consists of two granular rods of the same character as the re- 

 maining chromatin elements, while the other arm is composed 

 of two dense and homogeneous rods of smooth contour. All 

 these parts tend to diverge widely except at the level where the 

 unlike portions join, which is the point of fiber attachment in 

 the preceding cell generations and its site in the one to follow. 

 This difference in constitution is the reverse of the one in the 

 spermatogonium, but corresponds to the relative degree of con- 

 centration of the nuclear elements in the first spermatocyte 

 prophase. The interval betw^een the two spermatocyte mitoses 

 is very brief and the chromosomes may be followed thi'ough their 

 changes without any loss of identity. 



The metaphases of all second spermatocytes show eleven 

 separate chromosomes of which one is a V. On observing these 

 V-chromosomes (figs. 63, 64, pi. 7), however, it is found that they 

 are of two sizes which correspond in proportion to the two V's 

 of the spermatogonium and to the two of the first spermatocyte 

 anaphase. Upon division these are distributed to the spermatids 

 which are accordingly of two classes, equal in number. It is clear 

 from this very e\ddent history of the two V-chromosomes that 

 they go into different spermatozoa and so, upon fertilization, 

 are contributed to different individuals. Of some theoretical 

 interest is the fact that the rod -shaped homologue joined to the 

 accessory chromosome has a criss-cross inheritance while its 

 V-mate is confined to the male line. The presence of the ac- 

 cessory chromosome as a portion of one V means the addition of 

 one chromosome to the count of eleven separate elements, and 

 so conforms to the conditions in other Orthopteran species. 



IV. GENERAL CONSIDERATIONS 



The very extensive and detailed studies of chromosomes which 

 have been in progress for many years would not be fully justi- 

 fied if the result were merely a record of interesting but non- 

 significant protoplasmic manoeuvers. It is the belief that the 

 substances of the chromosomes are specific materials which are 

 intimately concerned ^^1th the development of a multitude of 



