REPORT ON THE CIRRIPEDIA. 3 



resemblance to that of Scalpellum peronii. Whereas the parasites in the first three 

 species (Scalpellum vulgare, Scalpellum ornatum, and Scalpellum rutilum) are in such 

 an extraordinarily modified and embryonic condition, that they can hardly be compared 

 with other Cirripeds, those of the other three (Scalpellum peronii, Scalpellum rostmtum, 

 and Scalpellum villosiim) are pedunculated Cirripedia, remarkable for their sinallness. 



These are the facts which were known to Darwin ; he then enters into a masterly 

 discussion of the evidence that these parasites are really the males of the Cirripedia to 

 which they are attached. Curious and novel as was the fact, his reasoning was so con- 

 vincing that this theory has been generally accepted. 



With respect to the occurrence and the structure of these complemental males, I believe 

 I have been enabled to augment our knowledge not inconsiderably. Though the princi- 

 pal result of my investigations has been to convince me of the exactness of Darwin's 

 theory, I think the question is important enough to justify me in giving all the informa- 

 tion which I possess in the following pages. 



I observed the complemental male in nineteen out of the forty-one new species of 

 Scalpellum described in my Keport. 1 I found them all in or about the same place, 

 viz., at or near the occludent margin of the scutum at the interior side of this valve, a 

 little above the adductor muscle. As a rule they are placed in a pouch formed by the 

 mantle ; very often, but not always, I found them on the left as well as on the right 

 hand scutum. In five different species I took either from one or from both scuta two 

 or more specimens, in the other species each, or one only, of the two scuta was furnished 

 with a single male. In one species (Scalpellum marginatum) the male was seated at a 

 considerable distance from the occludent margin of the scutum, and hence it happened that 

 at first I did not find it out. In one species (Scalpellum recurvirostrum) the only male 

 observed was still in the Cypris-larval or pupa stage ; in three other species (Scalpellum 

 regium, Scalpellum eximium, and Scalpellum velutinum) males in the pupa stage were 

 attached along with full-grown males. The male of Scalpellum brevecarinatum could 

 not be studied, being in a very unsatisfactory condition. 



In eighteen out of the nineteen cases I was able to form an opinion as to the condition 

 of the male when the testis was ripe, and the little creature therefore full-grown or nearly 

 so. In five of these eighteen cases the condition can be said to correspond with that of 

 the male of Scalpellum vulgare. In thirteen the males are still more degenerate. These 

 five are Scalpellum tritonis, Scalpellum intermedium, Scalpellum parallelogram >i w , 

 Scalpellum elongatum, and Scalpellum triangulare. I think they correspond with 

 Scalpellum vulgare in as far as there are. rudimentary valves visible in them. The 

 thirteen remaining species all, no doubt, belong as regards the structure of their males 



1 Zool. Chall. Exp., part xxv. The small species represented by single specimens have not been investigated so 

 thoroughly as would have been necessary to make out whether a male really occurred or not. I often found mysell unable 

 to do so without spoiling the specimen. 



