56 THE VOYAGE OF H.M.S. CHALLENGER. 



way for the frequent occurrence of spermatophores glued to the back of the female, 

 usually on the penultimate thoracic ring. This I have seen so often, that 1 came to 

 recognise the females of the species, under the hand lens, by that character alone. It is 

 obvious tli.it the fixture of a spermatophore in that situation must be an entirely futile 

 proceeding, but it is equally evident, from the abundance of the species, that plenty of 

 spermatophores must get properly located. The males of Undina darwinii are extremely 

 abundant, and must, if we take as a law the proportions of the sexes amongst other 

 Copepoda, and especially amongst the species of the nearly allied genus Euchceta — be far 

 more than sufficient for the impregnation of the females. The competition for females 

 will thus be very severe, and in the heat of the chase it seems very possible that mis- 

 carriages of the kind referred to may often kapjjen. If this explanation be fanciful 

 or wide of the mark, the fact of the common malposition of the spermatophores is, 

 at any rate, an interesting one. 



Scolecithrix, 1 n. gen. 



Undina, Lubbock (in part) Trans. Entom. Soc, 1856. 

 (?) Undina, Claus, Die frei lebenden Copepoden, 1863. 



Head and thorax coalescent, rostrum short and furcate, posterior ventral angle of 

 cephalothorax somewhat produced. Anterior antennae in the female twenty to twenty-three- 

 jointed, in the male nineteen-jointed, not geniculated. Mandibles well developed. Inner 

 branch of the maxilla very small. Inner (secondary) branch of the posterior antenna 

 longer than the outer, its first joint imperfectly divided near the base, tw T o small joints 

 intercalated between it and the terminal joint. Anterior foot-jaw bearing at the apex, 

 instead of the usual curved setae, a bunch of thick flexuous (sensory ?) filaments. 

 Posterior foot-jaws nearly as in Calamus. Inner branches of the first pair of feet one-, 

 of the second two-jointed, of the third and fourth pairs three-jointed, the first joint 

 in all cases very small. Fifth pair of feet in the female wanting or rudimentary, 

 in the male elongated and prehensile. Abdomen in both sexes four-jointed ; no long 

 tail seta. 



Claus states that the first pair of foot-jaws in the male Undina messinensis are obsolete. 

 This is certainly not the ease in the typical Undince, nor is it so in the species which I 

 have here referred to the new genus Scolecithrix. If it be really so in Undina messi- 

 nensis, another genus must be established for the reception of that species, unless, indeed, 

 it be referable to Euchceta. Another important difference, noticed by Claus, is in the 

 structure of the posterior antenna?, the outer branch of which is very much smaller than 

 in any species of Undina or Scolecithrix known to me. 



1 ffxaTinl, a worm ; 0gi|, hair. 



