24 rROCEEDINGS OF TEE NATIONAL MUSEUM. vol. 53. 



and forms a pit or shallow depression. In Ilaemohaphes the pro- 

 boscis is apparently confined to the mouth tube proper and the max-, 

 allae are attached to the ventral surface of the head at its base. 



The mandibles are simply curved claws or spines, one- jointed and 

 entirely devoid of teeth. The first maxillae are also one- jointed and 

 armed with short setae; the second maxillae are tAvo or three jointed 

 and terminate in one or two stout claws. There is also usually a 

 stout spine on the inner or outer margin of the basal joint. These 

 appendages are important organs of prehension in the copepodid 

 larvae, and doubtless assist in the burrowing of the female into the 

 flesh of her final host. 



The maxillipeds are found in both sexes of Lernaea^ but so far as 

 known only in the males of other genera, and are made up of a 

 large swollen basal joint, a smaller distal joint, and from one to 

 five terminal claws. 



The swimming legs, as Claus pointed out, do not increase in size 

 from the larval condition and, therefore, appear rudimentary and 

 degenerate upon the greatly enlarged body of the adult. There is, 

 however, no actual degeneration or retrogression in their structure, 

 but it often, perhaps usually, happens that the rami or even the 

 entire legs get broken off. This may result either from the move- 

 ments of the parasite itself or during its removal from its host 

 and subsequent separation from the cyst which envelops it. But 

 in such cases there is always left the scar at either end of the chitin 

 rib which connected the legs or the stumps of the rami. AVe can not, 

 therefore, regard the swimming legs as having actually degenerated 

 or retrogressed, but simply as having failed to increase in size with 

 the rest of the body. And we must not conclude from an examina- 

 tion of one or two specimens that the legs are destitute of rami, when 

 further search will likely yield a specimen on which they are still 

 retained. 



In general we may say that the genus Lernaea possesses five pairs 

 of sAvimming legs, of which the first four pairs are biramose Avith- 

 three-jointed rami, while the fifth pair is uniramose and unseg- 

 mented. 



In most of the other genera there are but four pairs, even in the 

 larval form — the first tAvo pairs biramose, the third and fourth pairs 

 uniramose, all the rami two-jointed. In Perodcrma and Sarcotretes 

 there are but three pairs — the first tAvo pairs biramose, the third pair 

 uniramose, and all the rami two-jointed. In Uaemohapholdcs there 

 are only two pairs of legs, both biramose with tAvo-jointed rami. 



The copepodid larvae of Sarcotretes possess only three pairs of 

 swimming legs in contrast to the four pairs found in the larvae of 

 Lernaeocera and Pennella, and the five pairs in the larvae of Lernaea. 



