346 THE ZOOLOGIST. 



Hemel Hemstead, Chipperfield Common Pool, Langleybury Pool, 

 Chesham Eoad Pool, Ashley Green Pool, the Chess near Piick- 

 mansworth, Boxmoor Common Pool, and various brooks near 

 the canal. 



For identification purposes, one of the most important 

 structural features of specimens of Cyclops is that of the fifth 

 pair of feet. In most cases, the determination of their structure 

 demands some care and patience, but in specimens of gigas this 

 determination is unusually easy and can be made without the 

 need of dissection. Fig. 32 was drawn from a narcotised speci- 

 men as it lay on its back under favourable illumination. 



The largest specimen of which I have any reliable measure- 

 ments was obtained from the small pool on Boxmoor Common, 

 from which the rotifer Hydatina senta was obtained, as has been 

 stated already. The specimen of gigas was one of a fairly large 

 number, all females, dredged from the pool on October 16th, 

 1912. From the tip of its cephalo-thorax to the ends of its 

 longest tail-setse was 4*5 mm. or above ^ in. 



The greatest numbers of specimens obtained on one occasion 

 were taken from the inner moat, Berkhamsted Castle, on 

 June 3rd, 1913, and July 21st, 1913 ; from Frithesden Pool on 

 October 3rd, 1913 ; from Parsonage Farm Pool on December 

 19th, 1912, March 24th, 1913, July 21st and July 27th, 1915 ; 

 from Langleybury Pool on August 20th, 1915, and Septem- 

 ber 4th, 1915 ; from Boxmoor Pool on October 16th, 1912; and 

 from a small pool near Ashley Green on July 21st, 1913. The 

 rest of the collections made on many other occasions from 

 these and other localities usually consisted of one, two, or not 

 more than five specimens. 



Ova-bearing females have been obtained in every month of 

 the year, but they have been most plentiful in March and July. 

 Males have been obtained in greatest numbers in February, 

 March, July, and September; March seems to have given the 

 best results. 



The usual colour of the marginal parts of the cephalothorax 

 {the central parts being brown or black from the presence of the 

 alimentary canal) was green, brown, bluish, or dull grey. The 

 ovisacs were usually green, brown, or grey of various shades, 

 but most often dark ; sandy ovisacs, also, have not been rare. 



