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 
odgenesis, 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 with 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 in 
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 o6gonia, 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- 
