REPORT ON THE COPEPODA. 59 



And I cannot suppose that the female would lose its fifth pair of feet in a more advanced 

 stage of development, which must be the case if it be really a young Scolecithrix dance. 

 Moreover, had it belonged to that species it would almost certainly have been noticed in 

 some of the many gatherings in which Solecithrix dance occurred. 



Euchceta, Philippi. 



Euchceta, Philippi, Archiv. f. Naturgeseh., 1843. 



„ Dana, Proc. Amer. Acad. Sci., 1849. 



,, Claus, Die frei lebend. Copep., 1863. 

 Euchirus, Dana, Amer. Journ. Sci. 



Head and thorax coalescent. Anterior antennae twenty-four-jointed, those of the 

 female provided with a few very long setae, those of the male scarcely geniculated and 

 bearing much shorter setae. Forehead elongated, triangular, rostrum transversely notched 

 or simply curved, not furcate. Eyes small, simple. Mandibles well developed in the 

 female, biting portion wanting in the male. Maxillae abnormal, the two branches almost 

 coalescent, in the male very minute. Anterior foot-jaws short and stout, strongly 

 setiferous, obsolete or entirely wanting in the male. Posterior foot-jaws very long and 

 well developed, doubly geniculated and conspicuously projected from the body, very 

 small in the male. Inner branch of the first pair of swimming feet one- (or two-) jointed, 

 of the second pair one-jointed, of the third and fourth pairs three-jointed. Fifth pair 

 wanting in the female, in the male much elongated, both limbs prehensde. Abdomen in 

 the female composed of four, in the male of four or five segments ; tail setae in the male 

 nearly equal, the second seta of the female, on each side, usually very long. 



The eyes were not seen except in one or two of the specimens, having been mostly 

 obliterated by immersion in alcohol, but from an indistinct glimpse of them in these 

 examples they seem to be very minute, and situated almost immediately behind the 

 rostrum. The last very minute joint (twenty -fourth) of the anterior antenna (in Euchceta 

 prestandrece) is called by Claus a tubercle, but I am unable to see any structural distinction 

 between it and the other joints. The absence of the biting segment of the male mandible 

 is a very remarkable, and, so far as I know (with the single exception of Calanoides, a new 

 genus described further on), a unique character amongst the Gnathostomata. It is not 

 noticed by Claus or by any other author, but I have carefully dissected many specimens 

 of Euchceta prestandrece and other species, and have never been able to find a trace 

 of that structure, except in the case of Euchceta austral is, where there is a doubtful rudi- 

 ment of it. The very feeble development of the male maxillae and foot-jaws, together with 

 the absence of the mandible, and sometimes also of the first foot-jaw, points perhaps to the 

 conclusion that the life of the creature is a very short one, death possibly following 

 speedily the act of copulation. We seem to have here a case of retrograde development, 



