NATURAL HISTORY OF BHOMPSTON POND. 215 



food it contains) gives rise to two diverticula (f), and, passing 

 through the body, ends at the telson (g). This terminal part 

 of the abdomen bears no appendages, but is furnished with 

 two long tactile setae (h), and ends with two styles (i) repre- 

 sentative of the caudal fork. Within the carapace is a 

 coiled tube the shell-gland (j), or typical nitrogenous 

 excreting organ of the Entomostraca, opening to the exterior 

 near the second maxilla. The large spherical compound eye 

 (k), usually seen in a constant state of trembling, consists of a 

 relatively small number of retinulse, readily recognised even 

 under a low power. It is formed by the fusion of two 

 originally distinct lateral eyes ; these can only be seen separate 

 in the young (1). 



In the female there is a brood-pouch (m) between the 

 carapace and the dorsal surface of the body, in which the 

 summer (parthenogenetic) eggs develop. The layer of 

 winter eggs, protected by the ephippium (a modification of 

 the brood-pouch), are thrown off at the following ecdysis, 

 and, floating away, are able to survive the winter and 

 re-establish the species the following year. The eggs or 

 young, plainly visible through the carapace, are retained in 

 the brood-pouch by prominences on the shell and abdomen 

 (n, n). The males are recognised by their longer antennules 

 and absence of a brood-pouch ; they are smaller and rarer 

 than the females, but become more numerous in autumn or 

 when the environment becomes unfavourable. 



About one-half of the size of the water-flea is the closely 

 allied Ceriodaphnia reticulata (fig. 49). In this animal the 

 ridges on the carapace are arranged so as to form a large 

 number of polygonal areas, giving the whole a net-like appear- 

 ance. Behind the head there is a dorsal depression of the 

 carapace (a), while posteriorly there is a medial dorsal pit (b), 

 perhaps corresponding to the " dorsal organ " of some species 

 of Daphnia an organ used for fixing the resting animal to 

 weeds, &c. The antennules are short and movable in the 

 female ; the antennae (c) are relatively smaller than those of 

 Simocephalus, and the carapace terminates posteriorly in a 



