BRANCHIOPODA. ]31 



effects its first change of tegument, and repeats the same process 

 every five or six days, according to the increased or diminished 

 temperature of the weather; it is not merely the body and valves 

 which lose their epidermis, the branchiae and setae of the oars under- 

 going the same operation. It is only after the third change that 

 they are fitted to continue their species. At first the female lays 

 but a single eg^, then two or three, gradually augmenting the num- 

 ber, which in the D. magna amounts to fifty-eight. The day after 

 she has produced her ova, the female changes her skin, and in the 

 teguments which she abandons may be found the shells of the eggs 

 she has previously laid. The next moment anew batch is produced. 

 The young from each set of eggs are generally of one sex, and it is 

 rare to find two or three males proceeding from that which produced 

 females, and vice versa. But in five or six of these broods, in the 

 summer, one at most consists of males. Individuals are frequently 

 remarked, whose integuments are of a milky white, opaque and 

 thickened; they do not however appear to be affected by it, and on 

 the renewal of the shell, but slight rugous traces of this alteration 

 are perceptible. 



These animals cease to propagate, and no longer cast their skins 

 on the approach of winter; they perish before the extreme cold has 

 arrived. The ova contained in the ephippia, and which were laid 

 during the summer, are hatched on the first approach of the vernal 

 heat; and the ponds soon abound again with countless Daphniae. Some 

 naturalists attribute the occasionally sanguine tinge of these waters 

 to the presence of myriads of the D. pulex, but Straus says he never 

 remarked the fact, and that this species is at all times but slightly 

 coloured. Morning and evening, and even during the day in cloudy 

 weather, they keep on the surface; but in the heat of summer, or 

 when the sun darts his rays directly upon the pools which they inha- 

 bit, they descend to the depth of six or eight feet; frequently, not 

 one is to be seen on the surface. Their mode of natation is by little 

 bounds, of a greater or less extent, according to the length of their 

 oars, and in proportion to the projection of the shell which covers 

 the body, an increase of its size impeding their movements. Ac- 

 cording to Straus, their food consists exclusively of small parcels of 

 vegetable substances which they find at the bottom, and frequently 

 of Confervas. They always refused the animal substances he pre- 

 sented to them. He repeatedly saw them swallow their own faeces, 

 carried along by the current formed by the action of their feet, which 

 directs their ordinary aliment towards their mouth. They use the 

 hooks which terminate the extremity of their tail to clean their 

 branchiae. 



Daphnia pulex; Monoculns pulex, L. ; Pulex aquaticus arbores- 



