BNTOMOSTBACA. 



277 





the body, forcing the water into the brood-cavity, and again 

 expelling it through a wide orifice. These root-barna.cles 

 recall the Trematode worms, though the 

 latter are much more highly organized. 

 An allied form (Cryptophialus minuhis) 

 undergoes the larval or Nauplius stage 

 -=i!i™--p ^""^ in the egg, hatching in the pupa condi- 

 Fig. -m.-saecuiina car- tion, while another form (a species of 

 ?fto™'r»gfoV''e1ri? Peliogaster?) also leaves the egg in the 

 Thillben.^™" ^"'^'^ pupa form. 



Order 2. Entomostraca (Water-fleas). 

 — The type of this group is Cyclops (Fig. 331, G. serru- 

 latus F. see also Fig. 233) in which the body is pear- 

 shaped, with a single bright eye in 

 the middle of the head ; two pairs 

 of antennae, used for swimming as 

 well as sense-organs ; biting mouth- 

 parts, and with short legs. The 

 sexes are distinct, the females swim- 

 ming about with two egg-masses 

 attached to the base of the ab- 

 domen. The young is a Nauplius, 

 much like that represented in Fig. 

 229, the mouth-organs, the legs 

 and abdominal segments arising 

 after successive moults, until the 

 adult form is attained. Allied to 

 Cyclops is Cantliocamptus caver- 

 narum Packard (Fig. 233), an eyed 

 species, living in Willie's Spring, in 

 Mammoth Cave. 



Many Entomostraca are parasitic, 

 and consequently undergo a retro- 

 grade development, losing the 

 jointed structure of the body, the 



appendages being more or less .'^'^e- ^'i-oyciaps. «, eye: a, 

 aborted, while the body increases ^& '"' '"'"' ^' ''''-^"" 

 greatly in size. Such are the fish-lice, represented by the 

 Lemma of the cod. 



