THE ENTOMOSTRACA OF EPPING FOREST. 273
A glance at the above will be sufficient to show that, taking
the Cladocera as a whole, there are, in each year, two seasons of
exceptional activity in the production of the sexually mature
individuals. The sexual season par excellence is evidently the
autumn, October being the month of greatest activity, but in
addition to this there is also a period of moderate activity in the
spring, reaching its maximum in May. The number of species
affected in the latter case, however, is very limited.
Looking to the individual species we find that, although for
the majority the sexual period is confined to the autumn, some
of the forms are affected during both periods, e.g. Ceriodaphnia
megalops (?), C. quadrangula (?), Simocephalus vetulus, A lanella
excisa (?), and Chydorus sphaericus. Others, again, appear to
have only one annual sexual period in the spring, e.g. Daphnia
magna, D. obtusa, and Alona quadrangularis (?), whilst in the case
of Daphnia longispina (including D. lacustris), there seems to be
continuous sexual reproduction in progress from May to
October, although it is much more pronounced in the latter
month than at any other time.
So far as I can make out from the present records, it seems
certain that the colonies of the same species inhabiting different
pieces of water, behave very differently in this matter of sexual
reproduction. Thus in the case of Simocephalus vetulus, the entries
for which show two clearly defined periods, one in May and the
other in October, it is only in ponds of small size that males
and ephippial females have been found at all. This is most
decided in the case of the spring period, all the records having
been from quite tiny ponds or ditches. The size of the ponds
was on the whole somewhat larger for the autumn records, but
even in these cases the largest were the "Hollow" and the
"Shoulder of Mutton" ponds. On the other hand, this species
runs practically without a break through the three years' records
from the "Perch" pond and yet never once yielded a male or an
ephippial female. The same negative evidence is offered also
by the "Lake" Wanstead Park, the "Heronry" pond and the
Higham Park lake, but the records from these are not so con-
tinuous, and therefore not so convincing. The facts again in
the case of Chydorus Sphaericus, which also shows two sexual
periods, one culminating in April and the other in November,
are very much the same as in that of the foregoing species. The
records of males and ephippial females during the earlier period