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 rutilwn) arc in such 
an extraordinarily modified and embryonic condition, that they can hardly be compared 
with other Cirripeds, those of the other three ( Scalpellwn peronii, Scalpellwn rostratum, 
and Scalpellwn villosum) are pedunculated Cirripedia, remarkable for their smallness. 
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 Report . 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, Scalpellwn parallelogramma, 
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 myself unable 
to do so without spoiling the specimen. 
