DAVIS: SPERMATOGENESIS. 141 



Although the chromosomes seem 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 jNIoore 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 Marechal (:04, :05), who finds 

 that in the oocytes 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 Moenkliaus (: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 spermatoc\i:es. Baum- 

 gartner (:04) has found that in Grvllus autosomes in the form of rings, 

 crosses and rods constantly occur and that there is probably a fixed 

 nimiber 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 t\^e, although the number 

 and form of the different tv]:)es varies widely in different species. They 

 conclude: "What appears to us of first importance is the recognition 

 of the actual existence of permanent structural t\^es in the gemini of 

 different forms. Secondly, it would appear that in any particular 

 form the number of gemini of each t^^e have a constant numerical 

 relation to each other. Thirdly, so far as the investigation has at 

 present gone certain tvjDes of gemini appear to be common in all the 

 widely sundered forms." 



In Dissosteira there is a similar constancy in the different t^^es 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 



