FAUNA OF THE CHESS AND GADE. 341 



colourless, and in one specimen, obtained from Langleybury 

 Pool on February 3rd, 1916, the ovisac was bright red. 



The manner in which the number of specimens of G. staphy- 

 linus varies at different parts of the year is very striking. One 

 series of records will illustrate this. Langleybury Pool did not 

 yield a single specimen on August 20th, 1915, although the pool 

 was almost entirely covered by a thin film of bright green 

 duckweed. The pool was swarming with specimens of another 

 Entomostracan, Daphnia rotunda, and there were but few 

 Copepods. On September 6th, 1915, after a very careful 

 examination of two water samples, two specimens of C. staphy- 

 inus were obtained, both males. Another collection taken on 

 September 11th, 1915, yielded only three specimens. The next 

 collection was made on November 20th, 1915, beneath a thin 

 coating of ice. Hundreds of specimens were obtained, very 

 many with spermatic tubes attached, and a rather large number 

 with ovisacs ; a small proportion of the specimens, about a 

 tenth, were males. There must have been many millions of 

 specimens of C.staphylinus in Langleybury Pool on that November 

 day, but not one specimen of D. rotunda was obtained. On 

 August 20th, 1915, as already stated, no specimens of G. staphy- 

 linus were obtained, so that between August 20th and November 

 20th vast numbers of D. rotunda disappeared and were replaced 

 by vast number,s of C. siaphylinus. 



Numerous specimens of C. staphylinus have also been 

 obtained from Berkhamsted Castle Moats, Cholesbury Common 

 Pool, Parsonage Farm Pool, and from a small pool near Ashley 

 Green, but the periods of the year when the largest collections 

 have been made have not been the same as those given above 

 for Langleybury Pool. In the year 1913, for instance, only two 

 specimens were obtained from Langleybury Pool on June 18th, 

 but a large number was collected from the moats on June 3rd, 

 and while Langleybury Pool furnished many specimens on 

 November 12th, only a few were obtained from the moats on 

 November 21st. Again, in May, 1914, many specimens were 

 obtained from Langleybury Pool, and only a few from the 

 moats. 



The pools of Chipperfield Common, Leverstock Green, 

 Chesham Koad, Frithesden, and Hastoe have furnished speci- 



