418 THE ZOOLOGIST. 



specimens, and these differences are more striking when it is 

 borne in mind that Chipperfield Common Pool presents more 

 uniform conditions from year to year than most other pools in 

 the district. It seems that in 1912 the time of appearance of 

 large numbers of adult specimens of C. serrulatus in this pool 

 was in September, but in the year 1913 it was in the beginning 

 of August. 



2. The possible conditions favouring the occurrence of large 

 numbers of C. serrulatus. — With respect to the numbers of 

 specimens obtained, different localities in the country of the Chess 

 and Gade, as stated already, have given very different results. 

 A large number, however, have often been taken at a single 

 dredging from the pools of Chipperfield Common, Parsonage 

 Farm, Langleybury, Frithesden, Boxmoor Common, Chorley 

 Wood Common, Whelpley Hill, Cholesbury Common, Coxpond 

 and Wigginton, from the Berkhamsted Castle Moats, and from 

 the Chess at The Moor, Chesham, and the Gade at Great 

 Gaddesden. There are other localities for which the yields have 

 been very poor. Two of such localities, viz. Chesham Pioad 

 Pool and Bedmond Pool, have yielded, on many occasions, only 

 a few specimens or none at all. Other pools which may be 

 mentioned are those at the brick-kilns, Tyler's Hill, east of 

 Chesham, Hastoe Pool, and Aldbury Pool. From these three 

 pools only a comparatively small number of collections have been 

 made ; the pools at Tyler's Hill, it may be said, are not attrac- 

 tive to collectors since, as far as my experience goes, their 

 waters are covered by a film of soot. Of Chesham Eoad Pool and 

 Bedmond Pool I can speak with greater confidence, for many 

 water samples have been taken from them, and it seems strange 

 that they have given such poor results. 



Cyclops serrulatus certainly does not seem to be particular as 

 regards its habitat. Height above sea-level, depth of the water, 

 nature of the water, and its situation with respect to sun and 

 wind no doubt influence the life of the Copepod to some extent, 

 but in the country of the Chess and Gade they do not seem to 

 have much effect. Wigginton Pool, 700 ft. above sea-level, 

 has yielded numerous specimens, and so has Langleybury Pool, 

 which is 500 ft. lower ; many specimens have been taken from 

 water pure enough for Perch and Trout, and from water foul 



