IN TIIE NORFOLK BROADS DISTRICT. 
65 
because the more species there are in each collection the more 
the individuals of each species must be spread about. 
Secondly, vve can learn the hatching periods of the species — 
that is the hatching out of the imagos — from the table 
showing the number of species captured each month. Thus, 
when we find that there is a rise in number of species in the 
spring, followed by a fall in number in the summer, and 
again by a marked rise in the autumn, we can conclude that 
there have been two definite hatching periods. This, of 
course, does not exclude the probability of some species 
hatching at other times, but it indicates that the majority 
of species appear in the imago state at two definite periods 
of the year, in the spring and in the autumn.* 
With this explanation it will be seen that the Hydradcphaga 
are most widely distributed in October, and that in September 
most of the species are in the imago condition. Although 
there is a spring hatching of species in April, when sixty-four 
of the seventy-six species are represented, the number of 
individuals at that time is either small or is contained in 
but a small proportion of the collections. Although after 
April some of the species apparently disappear, the process 
of distribution goes on uninterruptedly until the autumn. 
In the Palpicornia there is also a spring and an autumn 
hatching of the species. The process of distribution, however, 
differs materially from that of the Hydradepliaga ; whereas 
in the latter, distribution reaches its maximum in October, 
the maximum for the Palpicornia is in July, and whereas in 
the Hydradcphaga the spring hatching takes place at much 
fewer stations than the autumn hatching ; in the Palpicornia 
the spring and autumn hatchings take place at about the 
same number of stations. 
The difference in the process of distribution in the two groups 
is perhaps to be explained by the different mode of life in the 
two groups. The Hydradcphaga are, both in their larval and 
perfect states, animal feeders, living upon insects, entomostraca 
* The spring hatch of course includes the re-appearanee of a number of 
individuals which have hibernated, but there appears to be an emergence from 
the pupal instar of many of the species at this period of the year. 
VOL. VIII. 
F 
