2 f HE VOYAGE OF H.M.S. CHALLENGER. 



I. THE COMPLEMENTAL MALES OF SCALPELLUM. 



Since 1851, when Darwin issued the first volume of his Monograph on the Sub-class 

 Cirripedia, nothing has been published on the so-called complemental males of Scalpellum, 

 though the subject was far from exhausted by his treatment of it. The truth of this 

 assertion in no way diminishes the respect which we feel to be due to the labours of the 

 great master in this department of investigation as well as in so many others. For when 

 we consider that the methods of microscopic reseafch have been greatly improved in the 

 thirty years which have since elapsed, and that" the male of Scalpellum vulgare, which 

 Darwin investigated, has a size of only 0"7 mm., we can only wonder at the thoroughness 

 of the information which he has given, andsat the soundness of the conclusions at which 

 he arrived. 



When dissecting Scalpellum vulgare, Leach, Darwin observed one or more very 

 minute parasites on the margins of both scuta, close to the umbones. He dissected one 

 or two specimens and at first concluded that they belonged to some new class or order 

 amongst the Articulata. By repeated and more careful dissection he was able to make out 

 the general appearance of the animal, the form of the thorax and abdomen, the generative 

 system, the antennae and the mode of its attachment ; he found that the prehensile 

 antennse of the little parasite showed an absolute correspondence with the same organs 

 of the hermaphrodite Scalpelluvi vulgare, and that it belonged exclusively to the male sex. 

 From this knowledge, together with its fixed condition and its short existence, he thought 

 himself justified in provisionally considering the little parasite as the complemental male 

 of the Cirriped to which it was attached. 



The results of Darwin's investigation of the complemental males of the other species 

 of Scalpellum known to him are, shortly, the following : — The complemental male of 

 Scalpellum ornatum, Gray, sp., shows a close general resemblance to that of Scalpellum 

 vulgare ; but as Darwin had only dried specimens of that species, his description is not 

 30 exhaustive ; he found males of Scalpellum rutilum, Darwia, also, but in so extremely 

 decayed a. condition that they could not be examined. What Darwin considered to be 

 the complemental male of Scalpellum rostratum, Darwin, is a little animal constructed 

 like an ordinary Cirriped and furnished with a mouth, thorax, and cirri, enclosed in a 

 capitulum (with a carina and a pair of scuta), and supported on a peduncle of moderate 

 size. Specimens were found attached to the integument of the hermaphrodite in a 

 central line between the labrum and the adductor scutorum muscle. The copiplemental 

 male of Scalpellum peronii, Gray, sp., is a pedunculated Cirriped with a capitulum of 

 six valves, firmly cemented to the integument of the hermaphrodite in a fold between 

 the scuta, in the middle line a little below the adductor scutorum muscle. Finally, 

 the complemental male of Scalpellum villosum. Leach, sp., is attached in the same 

 position as that of Scalpellum, peronii ; it is also six-valved and it has a close general 



