342 THE ZOOLOGIST. 



mens, but the results obtained have been insignificant compared 

 ■with those obtained from Langleybury Pool. There is not much 

 duckweed in the pools thus yielding comparatively few specimens, 

 and duckweed is a very suitable aquatic plant for the rapid 

 development of C. staphylinus. 



3. Cyclops viridis, Jurine. — This is a very variable species, and 

 the numerous differences which have presented themselves 

 caused me much confusion, especiaHy when examining specimens 

 about fifteen years ago from the districts of Tring, Aylesbury, 

 Cheddington, and Dunstable. At that time Mr. Brady's 

 * Monograph on the Copepoda ' was my chief guide. Under the 

 name Cyclops gigas, Claus, he gives a description which applies 

 to the larger forms of C. viridis, Jurine. Following him, I used 

 to consider C. gigas to be a distinct species, and this was con- 

 sistent with the finding of numerous specimens, to which his 

 description applied, in nearly every pool from which water 

 samples were taken. There was no difficulty in identifying 

 them ; their large size, well-packed elongated and divergent egg- 

 sacs, the forms of their antennas and feet, and the relative 

 lengths of the tail-setae proved them to be specimens of C. gigas. 

 Sometimes, however, large specimens and also smaller specimens 

 were taken, all presenting the structural features of Brady's 

 €. gigas. Whether small or large, all of them seemed to be fully 

 developed, and many of the females carried egg- sacs. The small 

 forms seemed to have no right to the title gigas, for, compared 

 with the other forms or with many other Copepods, they certainly 

 were not giants. The doubts caused by the finding of apparently 

 adult specimens having the same characteristic features, but 

 differing greatly in size, were to a large extent removed when , 

 some years later, I was able to consult Mr. Brady's " Kevision of 

 the Freshwater CyclopidaB and Calanidae " in the * Nat. Hist. 

 Trans, of the Northumberland, Durham, and Newcastle Society, 

 vol. ii (1894), and also the writings of some other authorities. 

 Of these, some consider that both the small and the large 

 specimens are identical and do not even constitute varieties, 

 whereas Herrick and Eichard consider C. gigas to be a variety of 

 C. viridis, Jurine. Also, on p. 82 of the paper referred to above, 

 Mr. Brady says : " There is no sufficient reason for the separa- 

 tion of the two forms., C. gigas appears to be simply a very 



