422 THE ZOOLOGIST.. 



another was made on August 25th, 1912, and only one ova- 

 bearing female was obtained. Many other examples might be 

 given, all tending to show that the Copepod fauna of one and 

 the same pool varies considerably within even short periods. 



4. The occurrence of males. — I find that my rough notes are 

 not sufficiently detailed to enable me to make any reliable 

 generalized statement as to the months when male specimens of 

 C. serrulatus are most numerous. Usually in water samples 

 containing large numbers of this Copepod some males have been 

 found ; the largest number, however, of which I have any record 

 or remembrance was taken from a small brook near the first lock 

 on the way from Hunton Bridge to King's Langley on May 13th, 

 1913. There were plenty of ova-bearing females, but the males 

 greatly surpassed them in numbers. To show the variability of 

 collecting-results, the three following records may be given : 

 (1) Four males and twelve ova-bearing females from Parsonage 

 Farm Pool, on July 1st, 1915 ; (2) Many ova-bearing females 

 and no males from Langleybury Pool, on July 13th, 1915 ; and 

 (3) Two ova-bearing females and one male from Parsonage Farm 

 Pool, on July 27th, 1915. 



5. The occurrence of specimens of C. serrulatus differing in 

 form and size from the type. — It has been due chiefly to a desire 



to consider this interesting subject in detail that I have col- 

 lected so large a number of specimens of this Copepod. 

 Numerous water samples have been examined without finding 

 any specimens of G. serrulatus differing appreciably from the 

 type. A few of the samples, however, have furnished specimens 

 presenting interesting variations of form and size. 



In the Ray Society's Monograph (' The Free-swimming and 

 Semi-parasitic Copepoda of the British Islands,' G. S. Brady, 

 vol. i. 1878, p. Ill), a mountain form is referred to differing 

 from the typical serrulatus chiefly in its darker colour, and in 

 the less profuse ciliation of the various setae. On plate 22 of 

 the same volume is a drawing of a female of this mountain form, 

 and such drawing shows neither combs nor cilia. It may be 

 stated at once that I have not found a specimen of this form in 

 the country of the Chess and Gade, but several which tended 

 towards it. These specimens will be dealt with first. On April 

 8th, 1913, a few females with brown cephalothorax and green 



