ENTOMOSTRACA. 



27? 



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

 expelling it through a wide orifice. These root-barnacles 



recall the Trematode worms, though the 

 latter are much more highly organized. 

 An allied form (CryptopJiialus minutnz) 

 undergoes the larval or Nauplius stage 

 in the egg, hatching in the pupa condi- 

 tion, while another form (a species of 

 Peltog aster 9) also leaves the egg in the 



"Brehm's pupa form. 



Order 2. Entomostraca (Water-fleas). 

 The type of this group is Cyclops (Fig. 231, C. serru- 

 latus F. see also Fig. 232) 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 h 

 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 eg 

 after successive moults, until the 

 adult form is attained. Allied to 

 Cyclops is Canthocamptus 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 

 aborted, while the body increases 

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

 Lcrncea of the cod. 



. ssi. 6y<&. , eye, A 



heart : W' e S 8 ; /, feet.-Af tei 



