38 NATHAN FASTEN 



into a fully developed larval form, which immediately begins 

 an active hunt for its host. During this stage of its life history 

 the copepod does not feed, its nourishment being derived from 

 the yolk which it carries over from its embryorfic development 

 (figure i. y). 



The larva is minute in size, about 0.726 m. m. in length. 

 Running along each side of its dorsal surface are two well de- 

 fined brownish streaks of pigment. A characteristic x-shaped 

 copepod eye occupies the middle of the head (figure 1, e). 



The head is broad, elliptical, and bears the mouth parts and 

 a peculiar attachment filament. The mouth parts are situated 

 on the ventral surface and consist of the first antennae, the 

 second antennae, the mouth tube, stationed between the second 

 antennae, the mandibles, the two pairs of maxillae (the first 

 and the second), and the maxillipeds. The attachment filament 

 is located beneath the head, and is made up of two parts: — 

 (1) a broad circular, mushroom-like body whose position is 

 between the first antennae, and (2) a tube-like structure, which 

 makes its way backward from the posterior region of the mush- 

 room body as far as the eye, and then turns upward in one 

 circular loop, passing underneath the first part of the tube, and 

 continues to ascend until it reaches the level of the posterior 

 margin of the mushroom body, where it is attached to the 

 head (figure 1, a, f). 



The thorax has two segments and these bear the two biram- 

 ous swimming feet (Fig. 2 s. f. 1 and s. f. 2), which end in broad 

 laminated bases — the respective exopods and endopods. Each 

 exopod terminates in four long feathery setae, whereas the 

 endopods contain seven of these plumose structures. The feet 

 are operated by a system of strongly developed dermal muscles 

 situated along the dorsal side of the body. 



The abdomen is rather slender and contains three segments. 

 The last of these is supplied with four feather-like setae, as 

 well as three pairs of smaller seta-like appendages, that are 

 vestigial in character. 



The head and the first thoracic segments comprise the main 

 bulk of the copepod 's body. Figures 1 and 2 illustrate, respec- 

 tively, a dorsal and a ventral view of the free-swimming copepod. 



