lt>6 h. .1. SruL'RKiKliD ON EiNTOMuS I'RACA. 



the middle of JS'ovember, and from thence a very rapid fall to 

 January again. It thus takes eight months to rise from 

 minimum to maximum, but only half that time to fall from 

 maximum to minimum. The averages for the whole period 

 bring this out still more clearly, and the breaks already referred 

 to are reduced to one in March and one in August (see also upper 

 curve of diagram). These temporary retrogressions deserve a 

 few moments' attention. They may, of course, be due simply 

 to the accidents of collection, but it is also possible that they 

 do represent a real falling oft", if not actually in the number of 

 species, at least in the abundance of some, thus causing them 

 to be more easily missed. I am certainly inclined to take the 

 latter view, because in the first place the same breaks have 

 been found to occur in a more marked manner in the records 

 from a single pond (see middle curve of diagram), and secondly 

 because some reasons for the probability of such breaks can 

 be put forward. For instance, the decrease in March may 

 really arise from the fact that during February resting-eggs that 

 happen to be in particularly favourable situations hatch out 

 prematurely, only to be quickly killed by the later frosts or 

 lack of food. There is a good example of this in the case of 

 Geriodaphnia rohmda, one record of which is for the 28th Feb., 

 1891, though it was not seen again for at least three months. 

 I noted at the time that only a single specimen was found, and 

 also that it was a young one. Again the decrease in August 

 may be due to the great heat of that month, and the accompany- 

 ing lessening of the volume of water in most of the ponds. 

 Returning, however, to the consideration of the main features 

 of the yearly cycle, it must be noticed as a singular circum- 

 stance that the period of maximum development is coincident 

 with, or at most only slightly antecedent to, the principal 

 sexual period of the year, and further that the comparatively 

 high figures reached in June and July seem to be in close con- 

 nection with a subsidiary season of sexual activity. The true 

 import of these facts must, so far as I can see, remain more or 

 less a matter of speculation at present, but they suggest a 

 possible line of special investigation for the future. 



Having nov rjisposed of the chief results obtained from the 

 study of the Wt?,nstead Park Entomostraca, there remain for 

 examination onlyii few miscellaneous points of a more or less 



