410 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 99 



Fifth copepodid. Male: The subadult condition of this male is 

 l)atent in the 5-segmented urosome, which conforms in proportion and 

 arrangement exactly to that of the female of the same stadium. 



The fifth leg is comparable to that of the adult male. The longer 

 of the terminal setae is lateral. The structures of the seventh thor- 

 acic somite are the two setae of the sixth leg and two pairs of rows 

 of spinules, as in the adult. 



The metasome of the subadult male exhibits some diagnostic fea- 

 tures. The maxillipeds, while they are by far the most developed of 

 the mouth parts, lack the free, subcheliform terminal segment of the 

 adult. Two such maxillipeds (fig. 34, I, J) show the sequence of 

 development of this appendage at an early stage and a later period 

 within the same stadium. In the early copepodid of stage five, there 

 is no indication of the elongate terminal claw (fig. 34, 1). A globose 

 end segment is the forerunner of the claw, however, as is seen in the 

 second example where, under the cuticle, can be made out the features 

 of the adult condition, about to be uncovered by the imminent final 

 molt. 



In the swimming legs the spinous processes of the distal medial 

 corners of the second endopodite segments to be seen in the adult arc 

 here lacking. The segmentation of the rami and the complement of 

 spines and setae are identical with those of the adult. 



Length, exclusive of setae of the caudal rami, is about 1.4 mm. 



Fourth copepodid. The metasome has the degree of segmentation 

 seen in the adult. The rostrum shows very great development of the 

 lateral spines, these being equal to more than three-fourths of the 

 length of the central beak. The antennules, antennae, and mouth parts 

 are as in the adult female. Figure 34, K, shows the arrangement of the 

 mouth parts, the very large basal segment of the maxilla nearly ob- 

 scuring the much reduced maxillipeds. 



The swimming legs are 2-jointed and the complement of spines 

 and setae of the adult is not attained, as the following representa- 

 tion of the armature of these appendages demonstrates : 



First leg, exopodite: First segment — lateral spine; second seg- 

 ment — four spines, four setae. Endopodite: first segment — medial 

 seta ; second segment — one spine, six setae. 



Second leg, exopodite: First segment — lateral spine; second seg- 

 ment — four spines, five setae. Endopodite: first segment — medial 

 seta ; second segment — three spines, five setae. 



Third leg, exopodite: First segment — lateral spine; second seg- 

 ment — four spines, five setae. Endopodite: first segment — medial 

 seta ; second segment — three spines, three setae. 



Fourth leg, exopodite: First segment — lateral spine; second seg- 

 ment — four spines, five setae. Endopodite: first segment — medial 

 seta ; second segment — two spines, one seta. 



