DAVIS: SPERMATOGENESIS. 119 



was formerly supposed that such differences are largely accidental 

 and not of fundamental importance. It is only within recent years 

 that the significance of the variation in the size of the chromosomes of 

 the same species has been appreciated. Montgomery (:01) first 

 showed that in several Hemiptera some of the autosomes in the sperma- 

 togonia are distinguishable by their size, and that there are always 

 two of each size. He also showed that during the maturation divi- 

 sions the autosomes so divide that each spermatid contains one 

 member of each pair. Since probably a similar process occurs in 

 oogenesis, Montgomery concluded that one of each pair of autosomes 

 is derived from either parent. In the following year Sutton (:02) 

 elaborated this idea at considerable length. Sutton found that in the 

 spermatogonia of Brachystola magna there are twenty-two autosomes, 

 which can be arranged in pairs according to their size. He agreed 

 with Montgomery that during maturation the members of each pair 

 become separated, so that in the gametes there is only one autosome 

 of each size. The fusion of the male and female gametes during 

 fertilization results in a restoration of the original paired condition. 

 Recently a number of investigators have found similar conditions in 

 the germ cells of animals belonging to widely separated groups, but 

 the autosome pairs appear to be most marked in the insects, where 

 they are often shown Avith almost diagrammatic clearness. Baum- 

 gartner (:04) found that in Gryllus the autosomes can be arranged in 

 graded pairs, although in some cases the difference between the pairs 

 is very slight. A similar result was reached by Montgomery (:05) 

 in Syrbula. In this species there are twenty chromosomes in the 

 spermatogonia, which are evidently paired, and he was able to dis- 

 tinguish the three largest and three smallest pairs, but the remaining 

 eight chromosomes are so nearly of the same size that the individual 

 pairs could not be distinguished. Montgomery believed one of these 

 medium sized pairs to be allosomes. Stevens (:05) has shown that irr 

 two species of Aphis the ten autosomes can be readily grouped in five 

 pairs and she later (:06) obtained similar results in both sexes of a 

 number of additional species. In these insects, owing to the small 

 number of autosomes and their great variation in size, the paired 

 relation is shown with exceptional clearness. Wilson (:05'^) has found 

 a similar condition in the spermatogonia of several Hemiptera and he 

 (:06) has described in detail the autosome pairs in a number of addi- 

 tional forms. He also found a similar series of paired autosomes in 

 the oogonia^ and even in the follicle cells of the ovary; likewise in the 

 investing cells of the testis there is the same or a multiple series of auto- 



