ENT0M08TRACA. 



377 





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 miniUus) 



undergoes the larval or Nauplius stage 



'^'^W'"^^'' in the egg, hatching in the pupa condi- 



Fig. ■jsa.-saccuuna car- tion> while another form (a species of 



So^TieMngfoV^eSt Peltogastev?) also leaves the egg in the 



Thillben.^'"" ''"'™'' V^V^ form. 



Order 2. Entomostraca (Water-fleas). 

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

 latus F. see also Fig. 333) 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. 

 239, 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 

 aborted, while the body increases ciark.' 

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

 Lerncea of the cod. 



Fig. 2i\. — Cyclops, e, eye; h, 

 heart ; eg, eggs ; /, feet,— After 



