356 THE INVERTEBRATA 



sessile and covered by an invagination of the outer cuticle, which forms 

 a shallow chamber over them. 



Artemia salina (p. 359) and a few marine cladocera are the only 

 members of the class whose habitat is not in fresh water. 



Throughout the group, thick-shelled eggs capable of resisting 

 drought or freezing are produced by sexual reproduction. Often 

 there is also parthenogenesis, the eggs of which are usually thinner 

 shelled than those that are sexually produced (see p. 367). 



The name Phyllopoda, which is applied sometimes to the whole 

 class and sometimes to its members exclusive of the Cladocera, is 

 on account of this ambiguity best not employed in systematic 

 nomenclature. 



Order ANOSTRACA 



Branchiopoda without carapace ; with stalked eyes ; with antennae of 

 a fair size but not biramous ; with the trunk limbs numerous and all 

 alike; and with the caudal rami unjointed, and flat or subcylindrical. 



We may take as an example of this group, Chirocephalus diaphanus 

 (Fig. 236), one of its two British representatives. This creature turns 

 up from time to time in temporary pools of water in various districts. 

 It is about half an inch in length, transparent, and almost colourless, 

 save for the reddened tips of most of the appendages and of the ab- 

 domen, the black eyes, and often a green mass of algae in the gut. It 

 is incessantly in motion, swimming on its back. Its delicate appear- 

 ance, and the iridescent gleaming of the bristles on its appendages as 

 they are moved have earned it the name of the fairy shrimp. The body 

 is long, subcylindrical, and enlarged anteriorly to form the head^ upon 

 which the mandibular groove (p. 332) is conspicuous. The head has 

 in front a median eye and a neck organ (p. 342), and bears at the sides : 

 {a) the large, stalked compound eyes; (b) the antennules, slender, un- 

 jointed, and ending in a tuft of sense-hairs ; (c) the stout antennae^ tri- 

 angular in the female but in the male (Fig. 237) elongate, two-jointed, 

 and carrying on the inside at the base a complicated, lobed "frontal 

 appendage " which comes into play when the limb is used for clasping 

 the female ; {d) the mandibles, whose bases are prominent at the sides 

 of the head, while the remaining part of each of them is directed to- 

 wards the mouth as a process with a blunt, roughened end. Below, 

 the head bears {a) the large labrum which is directed backwards under 

 the mouth ; {b) the paragnatha, a pair of small, hairy lobes behind the 

 mouth; [c) the maxillules, a pair ot small triangular plates fringed 

 by long bristles ; {d) the maxillae, which are microscopic vestiges, each 

 bearing three spines. 



Behind the head come eleven thoracic somites which bear each a 

 pair of phyllopodia. Fig. 238 shows that these possess all the typical 



