422 CETJSTACEA. 



the conditions of life and nourishment are unfavourable. Before 

 the appearance of the males, hermaphrodite forms * sometimes make 

 their appearance with an organization which is half male and half 

 female. 



At the season when males are not present, normally in the spring 

 and summer, the females produce the so-called summer eggs, which 

 contain a large quantity of oil globules and are surrounded by a 

 delicate vitelline membrane. They develop rapidly within the brood- 

 pouch between the shell and the dorsal surface of the mother, and 

 after the space of only a few days give rise to a fresh generation of 

 young Cladocera, which escape from the brood-pouch. The embryonic 

 development takes place accordingly under extremely favourable 

 conditions, which depend upon the rich supply of food yolk in the 

 large eggs, and are sometimes favoured by the secretion of additional 

 food material within the brood-pouch. 



At the season when the males appear, the females, under the like 

 influence of unfavourable nourishment and independently of copu- 

 lation, begin to produce so-called winter eggs, which are incapable of 

 developing without fertilization. The number of these hard-shelled 

 winter eggs is always relatively small. They are, therefore, distin- 

 guished from the summer eggs by their larger size and the greater 

 quantity of food yolk ; and their origin in the ovary is accompanied 

 by much more extensive processes of absorption. 



The Daphnidce live for the most part in fresh water. Certain 

 species inhabit deep inland lakes, brackish water, and the sea. They 

 swim quickly, and usually with a jumping movement. Some of them 

 attach themselves to solid surrounding objects by means of a dorsally 

 placed organ of attachment, the cervical gland. When the body 

 is thus fixed, the swimming feet seem to be able by their vibrations 

 to set up currents in which small food particles are swept towards 

 the animal. 



Sida crystallina 0. Fr. Mviller. The six pairs of lamellar legs beset with 

 long swimming setas. The rami of the swimming antennae two- to three-jointed. 

 Daplmia pulex De Geer. D. sima Liev. Five pairs of legs, of which the 

 anterior are more or less adapted for prehension. One ramus of the swimming 

 antennas is three-jointed, the other four-jointed. Polyphemus pedicvlus De 

 Geer. In the lakes of Switzerland, Austria, and Scandinavia. Ecadne Nordmanni 

 Lov6n, North Sea and Mediterranean. Leptodora, Jiyalina Lillj., in lakes. 



* Compare especially W. Kurz, " Ueber androgyne Missbildung bei Clado- 

 ceren," Sitzungsber der Altad. der Wisscnsch. Wien. 1874. Also Schmanke- 

 witsch. 



