424 THE ZOOLOGIST 



fro in the segments. They were very small forms of life, oval, 

 about twice as long as they were wide, unicellular, and nearly 

 colourless. 



It has been stated already that the angle between the long 

 axes of the ovisacs is about 60°, i. e. when the female is 

 swimming in plenty of water, otherwise of course the angle 

 may be much less or greater. On September 14th, 1912, a 

 specimen was obtained from Chipperfield Common Pool with 

 the ovisacs nearly parallel instead of being inclined at the 

 usual angle. There was no doubt about its being C. serrulatus ; 

 its combs were clearly seen, and its antennae, &c, were those of 

 serrulatus. 



Most of the female specimens, fully developed and carrying 

 ovisacs, from the country of the Chess and Gade have been 

 about 125 mm. long from the tip of the cephalothorax to the 

 extremities of the longest tail setae. Occasionally specimens 

 decidedly smaller than these have been obtained. On October 

 5th, 1912, many small ova-bearing females were obtained, 

 together with some of normal size, from Chipperfield Common 

 Pool ; and on January 27th, 1914, many small females were 

 obtained from Whelpley Hill Pool, but small as they were their 

 combs and ovisacs were well-developed. From the Chess at The 

 Moor, Chesham, abnormally small ova-bearing females were 

 obtained on March 11th, 1913, and April 28th, 1913. The 

 average size of these was about 1 mm. There is another 

 peculiarity, to be referred to later, about the serrulatus of the 

 Chess at The Moor, viz. the very light colour of the cephalothorax 

 and the ova. 



6. Variations of colour of specimens. — Probably no fresh- 

 water Copepod presents more variety in the colours of its 

 cephalothorax and ovisacs than C. serrulatus, and in many 

 cases the contrast between the colours of these parts is a very 

 pleasing one. When speaking of the colour of the ovisacs, it 

 should be understood that reference is intended to the ovisac 

 with its full charge of ova, to which the colour is due, for the 

 ovisac itself is colourless and nearly transparent. Not less than 

 one half of the numerous ova-bearing females obtained from the 

 country of the Chess and Gade had a brown or yellow cephalo- 

 thorax and green ovisacs ; as regards the shades, that of the 



