34 



NATURAL HISTORY OF ARTHROPODS. 



I have seen pools of water red with Daphnias, giving the appearance of bloody 

 water. Such phenomena used to be terrible portents to European peasants, foretelling 



any sort of coming disaster. The water becomes 

 fairly thick with the animals, and all these thousands 

 and millions of beings come into life in a very few 

 weeks. 



When the the pools begin to dry up, or, in perman- 

 ent bodies of water, when winter approaches, a new 

 mode of reproduction comes in. Instead of what may 

 be called neu- 

 ter-females, true 

 males and fe- 



FIG. 42. Ephippium of Acanthocercus. 



males are produced from the summer-eggs, and 

 from the female are produced two true eggs. 

 These are enclosed in a hardened part of the 

 shell, called the ephippium or saddle. This con- 

 sists of the dorsal and lateral parts of both 

 valves, which become hardened and opaque, 

 and when the moult takes place these separate 

 from the rest of the shell and unite their free 



FiG.44.Lepto(h>rahyaiina. a '. Antennuise. a". An- 



tennse. e. Eggs. h. Heart, s. Shell, st. Stomach. 



i, 2, 3, 4, 5. Legs (sixth pair not shown). 



, enlarged. g . Brain, n. Heart. 



edges to enclose the eggs. In this case 

 the eggs lie until spring or wet weather 

 causes them to develop. The parent does 

 not necessarily die on producing these 

 eggs, but may return to the formation of 

 summer-eggs. The deep or open water 

 forms of Cladocera live, as a rule, through 

 the winter, while the shallow water forms, 

 and those inhabiting temporary pools, de- 

 pend on the winter-eggs for the preserva- 

 tion of the species from year to year. 



This order is divided into two sub- 

 orders, Gymnomera and Calyptomera. 

 The first is characterized by a small shell, 

 not enclosing the limbs, the legs small, 

 the respiratory appendages rudimentary. 

 It embraces the families PODONTID.E, with 

 two genera, in which the abdomen is short 

 and enclosed in the shell, while the an- 

 tennulas lie close to the head ; POLYPHEM- 

 ID^E, which has the abdomen elongate and 

 free, and the antennula? exsert and free ; 

 and the LEPTODORID^;, which has six pairs 

 of ambulatory feet (the other families 

 having but four pairs), the abdomen 

 greatly elongate and segmented, while the 

 respiratory organs are absent. Leptodora 



. , J 



is one of the most outre of the Cladocera. 



