Entomostraca ( Water-Fleas) , 



451 



abundant during the hot summer months when pools are most 

 subject to be dried up. Moreover, it is probable that in many- 

 cases the animals themselves would bear such a desiccation 

 without loss of life. Thus Dr. Baird "has found, upon ex- 

 amining* ponds which had been filled again by the rain after 

 remaining two months dry, numerous specimens of the Cyclops 

 quadricornis in all stages of growth." It seems, indeed, to be 

 almost a condition of existence with some species that their 

 habitats should be exposed to alternations of wet and drought ; 

 as for instance CkirocepJialus diaphanus. This, which is one 

 of the largest (being upwards of an inch in length), and cer- 

 tainly the most beautiful of Entomostraca, inhabits cart-ruts 

 and shallow pools mostly near the edges of plantations, but 

 never any, so far as I can learn, which are not liable to be dried 

 up easily. The Chirocephalus is rare in Britain, most of the 

 known localities for it being in the south of England. The 

 only living specimens I have seen were taken at Tillmire, near 

 York, the most northern point at which it appears to have been 

 hitherto found. Some species are much more susceptible of 

 cold than others. For instance, Polyphemus pediculus is killed 

 on the first approach of frost, while the Daphnice and Cyclops 

 may be found living the winter through, and, indeed, may be 

 positively frozen and yet recover. For the following interest- 

 ing table, exhibiting the effect of temperature on the species 

 of Entomostraca, I am indebted to the Rev. Alfred Merle Nor- 

 man. The table shows the number of species taken at a single 

 gathering in the same piece of water, during the successive 

 months of 1861 : — ■ 



January (after 



the intense 





July . 



. 14 species 



frost of 1860 



-61) . . 



4 species. 



August 



• . ■ ? » 



February 





7 „ 



September . 



• • 17 „ 



March . 



# # 



7 „ 



October 



• • 17 „ 



April 



, , 



17 „ 



November . 



. . 10 „ 



May 



. , 



10 » 



December . 



. . 12 „ 



June 



t • 



? „ 







Mr. Norman remarks that the deficiency in the May number 

 may perhaps arise from the day when the gathering took place 

 not having been fine, the animals for that reason withdrawing 

 into deeper water. While thus tolerant of all but very intense 

 cold, it is interesting to note that Entomostraca will also live 

 and thrive in water of very considerable heat. There is a re- 

 servoir connected with the engine of the Monkwearmouth col- 

 liery, the water of which is somewhat irregular in temperature, 

 but mostly sufficiently hot to steam profusely. On one occasion 

 I found the heat to be 100° Fahrenheit, and I suppose this may 

 be taken as about the general temperature of the water. A 

 pond-weed {Potamogeton perfoliatus), and a Callitriclie, grow 



