﻿16 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



There is a temptation to regard A. oryzaphagus and A. higgsi as 

 two clones, one characterized by 35 or 344-i and the other by 36 or 

 35 +i rings. In A. cancriformis, there might be clones with 33 and 

 with 34 rings. But such conclusions would be premature. There 

 is still the possibility that the small variation existing in a partheno- 

 genetic population is due to environmental influences. 



In both Lepidurus and Apus, parthenogenetic populations are 

 characterized by a relatively small number of rings. But there are 

 bisexual forms, too, with a similar niunber. 



It would be interesting to make comparisons with other groups of 

 many-segmented Arthropoda where parthenogenesis is laiown to 

 occur. In the Conchostraca we may expect something of this kind. 

 Species with a varying number of rings are known in the Conchostraca 

 Spinicaudata (Linder, 1945); and there is a species where a fixed 

 number is postulated and probable, though not definitely proved, 

 viz., Cydestheria hislopi Baird. The latter has both parthenogenetical 

 and bisexual propagation in the same population, changing its mode 

 of propagation according to the time of year; in other Spinicaudata, 

 where males often are veiy rare, parthenogenesis is likely to be found 

 in many populations (as in Limnadia). Further investigations are 

 highly desirable. 



Conditions of a similar kind occur in the Diplopoda, where they 

 are a little better known, but detailed comparisons may have to be 

 postponed until we loiow more of the variation in the Notostraca. I 

 wish to point out one feature, however, that was brought to my atten- 

 tion by Dr. Hans Lohmander: in the Diplopoda the parthenogenetic 

 forms are known to become sexually mature when having a smaller 

 number of rings than the bisexual ones. This reminds us of the fact 

 that parthenogenetic forms in Lepidurus and Apus also have rela- 

 tively few rings, although likewise having bisexual forms with just 

 as few or even fewer rings. Matters seem to be rather complicated 

 here. 



It has been maintained by Gaschott (1928, p. 277) that males are 

 relatively rare in cold districts and increase in number in warmer 

 parts of the world. It is, of course, a striking observation that 

 Lepidurus arcticus has very few males, or none at aU, in many popula- 

 tions, and that males are known to be common in tropical species. 

 The present material no doubt gives the impression that the principle 

 is acceptable, though with the reservation that we still know rather 

 little of the tropical notostracans. Rosenberg's find of partheno- 

 genetic populations in such a warm locality as California's rice fields 

 clearly shows that a cold cHmate is not necessary for the development 

 of parthenogenesis. 



