ENTOMOSTRAGA. 



397 



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 {Gryptophialus minutiis) 

 undergoes the larval or Nauplius stage 

 in the egg, hatching in the pupa condi- 

 Fig. w,.-saccuiina car- tion» while another form (a species of 

 S"L"t'lToVe!nngfortft Peltogaderf) also leaves the egg in the 

 Thillben.^™"" ^"^'' P^^Pa form. 



Order 2. Entomostraca (Water-fleas). 

 — The type of this group is CyclojJS (Fig. 236, C. quad- 

 ricornis, see also Fig. 237) in which the body is pear- 

 shaped, with a single bright eye in 

 the middle of the head ; two pairs 

 of anteunse, 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. 

 234, the mouth-organs, the legs 

 and abdominal segments arising 

 after successive moults, until the 

 adult form is attained. Allied to 

 Cyclops is Cantliocamptus cavcr- 

 narum Packard (Fig. 238), 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 

 Lemma of the cod. 



Fig. 236. — Cyclops, e, eye ; ^, 

 heart ; eg, eggs ; /, feet.— After 

 Clark. 



