DAVIS: SPERMATOGENESIS. 141 
Although the chromosomes séem to lose their identity during the 
resting stage, this must be only apparent, since in the prophase they 
reappear with the same orientation as before. Similar conditions 
have been described by Rabl (85) in Salamandra and Boveri (88) 
in Ascaris. Recently Otte (:06) has found that in the spermatogonia 
of Locusta each chromosome remains in a distinct vacuole during the 
resting stage, while Farmer and Moore (:05) have found in Peri- 
planeta, and Moore and Embleton (:06) in ‘Triton, that although a. 
common nuclear membrane is formed in the resting spermatogonia, 
the individual chromosomes can still be distinguished. Of interest 
in this connection are the results of Maréchal (:04, :05), who finds 
that in the odcytes of certain fishes the chromosomes gradually be- 
come less distinct during the growth stage owing to the fact that the 
chromatin travels out along fine threads, while the axis still remains 
distinct as a somewhat more deeply staining mass. 
Of especial interest are the results of Moenkhaus (:04), who was 
able in hybrids between Fundulus and Menidia to distinguish the 
chromosomes of either parent up to the late cleavage stage. Even 
more striking results have been obtained in plant hybrids. 
Evidence of still greater weight is furnished by the occurrence of 
bivalent chromosomes of constant form in the spermatocytes. Baum- 
gartner (:04) has found that in Gryllus autosomes in the form of rings, 
crosses and rods constantly occur and that there is probably a fixed 
number of elements of each type, while Nichols (:06) has described 
similar conditions in the spermatocytes of Oniscus. Recently Moore 
and Arnold (:06) have investigated a number of animals from this 
standpoint and find that in the spermatocytes of each form studied 
several types of bivalent chromosomes (‘‘gemini’’) occur, and that 
there are always a fixed number of each type, although the number 
and form of the different types varies widely in different species. ‘They 
conclude: “What appears to us of first importance is the recognition 
of the actual existence of permanent structural types in the gemini of 
different forms. Secondly, it would appear that in any particular 
form the number of gemini of each type have a constant numerical 
relation to each other. Thirdly, so far as the investigation has at 
present gone certain types of gemini appear to be common in all the 
widely sundered forms.” 
In Dissosteira there is a similar constancy in the different types of 
bivalent autosomes, and although in the other forms a similar detailed 
study of the autosomes was not made, yet where, as in Stenobothrus 
and Steiroxys, there are certain easily distinguishable elements, these 
