2 
THE 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 research 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, and at 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 
antennae of the little parasite showed an absolute correspondence with the same organs 
of the hermaphrodite Scalpellum 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 
so exhaustive ; he found males of Scalpellum rutilum, Darwin, 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 complemental 
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 
