FAUNA OF THE CHESS AND GADE. 417 



3. The occurrence of ova-bearing females. 



4. The occurrence of males. 



5. The occurrence of specimens presenting varieties of form 



and size. 



6. Variations of colour of specimens. 



1. Relative numbers of specimens at different times. — During 

 every month of the year numerous specimens (including im- 

 mature specimens) have been obtained. The identification of 

 the immature specimens is difficult and not always satisfactory ; 

 they seem, however, to be relatively most numerous in the month 

 of November, and they have also been relatively numerous in 

 the months of April and May. My records for the usually un- 

 inviting month of November are fewer than those for other 

 months, but the most noteworthy is one for November 12th, 

 1913, when thousands of immature specimens of Cyclops were 

 obtained from Langleybury Pool ; in many of these the combs 

 of C. serrulatus were just discernible ; not a single specimen 

 with ova was seen. In the same pool, on May 2nd, 1914, there 

 were numerous specimens of G. serrulatus, all except a few 

 being immature forms in the Nauplius stage or the Copepod 

 stage, and only one ova-bearing female was seen. On April 28th, 

 1913, numerous specimens in the Nauplius stage were obtained 

 from Wigginton Pool ; in this case, however, there were also 

 many ova-bearing females, and the birth of young ones was 

 proceeding rapidly. 



Taking account of adult specimens only, the largest numbers 

 have been obtained in August, September, and October, and 

 large numbers have been obtained in March, June, July, and 

 January. 



The above results are based on an examination of the records 

 as a whole. When the yields of any particular locality are 

 considered, it is found that they vary greatly from year to year. 

 Chipperfield Common Pool furnished only a few fully developed 

 specimens on August 2nd, 1912, but a very large number on 

 August 4th, 1913. Nearly a hundred specimens were obtained 

 on September 14th, 1912, and not one on September 15th, 1913 ; 

 a few were obtained on April 8th, 1913, and none at all on April 

 11th, 1914. The dates compared in each year are nearly the 

 same, but there were distinct differences in the yields of adult 

 Zool, 4th ser, vol. XIX. , November, 1915. 2 K 



