1148 Proceedings of Royal Society of Edinburgh, [sess. 
case of fecundation will get resting eggs, but otherwise commonly 
will remain barren. 
With regard to the derivation of these large females I think it 
most probable that they are derived immediately from the ephippia 
which in spring and during the few summer months will be 
hatched at quite different periods. If this holds good, the life 
cycle of the large females is as follows : 
The individuals hatched in spring produce a very large brood 
(c. 40 eggs), and later on broods of some 6-12 eggs. How many 
broods they produce I don’t know, but undoubtedly more than one. 
I have found females with big young ones in the incubatory part of 
the carapace, and with more than twenty dark eggs in the oviduct 
well separated from each other. How long the large females live 
is not known, but on 1st August I have found many with only 
one or two very large young ones (fig. 6) in the incubatory part, 
and these were always males. In the same sample were many 
barren females, and on 1st September almost all had disappeared ; 
the few I saw were all barren. On the other hand, large females 
with many eggs become common again, as stated above, at 18th 
September as well as in the following samples. 
As I have not myself made the collections, I will not draw 
the very obvious conclusion which the sample of 1st Septem- 
ber might occasion, but shall restrict myself to the above-cited 
results, which may be arrived at through direct study of the 
sample. My opinion of the life cycle may shortly be expressed 
as follows : 
During the time from May to November, the ephippia in 
different numbers will be hatched and the young ones — the first 
generation — very quickly grow out to large females, which 
commonly only propagate parthenogenetically, producing an un- 
known number of broods. The young ones — the second generation 
— derived from these females are males or sexual females, which 
pair and which ordinarily only produce resting eggs. D. longispina 
is in Myvatti jnonocyclic. 
To the above I shall add the following remarks : In two of the 
Danish lakes, the lakes of Yiborg and Hald, D. longispina appears 
in races very like the race of Myvatn. In the lake of Yiborg we 
also find the above-mentioned great females characterised by their 
