REPORT ON THE CIRRIPEDIA. 19 



dried, to demonstrate the absence of the vesicuke seminales and testes. The male animals 

 were lodged in a pouch on the under side of the scutum, and in that case should not bear 

 the name of "complemental" males. From the state of the specimens of ScalpeUum 

 rutilum, Darwin, which Darwin examined, it was quite impossible to ascertain whether 

 the individual was a hermaphrodite or a female ; from the analogy of its nearest congener, 

 ScalpeUum ornatum, the latter, Darwin says, is the more probable. 



Darwin's supposition as to the unisexuality of some species of ScalpeUum proves to 

 be in very striking accordance with the facts. What I at first considered to be the 

 hermaphrodite form of ScalpeUum regium (Wyv. Thorns.), Hoek, is not furnished with 

 a penis, and does not show a trace either of a testis or a vesicula seminalis. To 

 have full certainty in this respect, I divided the whole thoracic part of the body of a 

 specimen of this species into a series of sections, and in none of them did even the smallest 

 trace of a part of the male genital apparatus appear. The body was stained in toto by means 

 of aluminium carminate, a most brilliant staining for the testis and for the sperma- 

 tozoa within the vesicula seminalis when present. I then repeated the examination of 

 ScalpeUum vulgare, Leach; I found the animal a true hermaphrodite ; it is furnished with 

 a well-developed penis, and the vesiculse seminales have exactly the structure of these 

 organs in species of the genus Lepas. The only difference is shown in their small size. 

 Slightly more developed testes pour out their products into the vesicuke seminales. 



The specimen of ScalpeUum regium, of which I examined a series of sections, was a 

 full-grown animal ; it was furnished with males and there were ova in the ovigerous 

 lamellae. I got the same results when making a series of sections of ScalpeUum 

 parallelogramma, Hoek (PI. IV. fig. 9), and ScalpeUum nympliocola, Hoek (PL IV. fig. 10). 

 So I think that we may safely draw the following conclusions : — 



There are species of the genus ScalpeUum, Leach, which show a very characteristic 

 dimorphism. Some of these consist of large hermaphrodite and small rudimentary 

 male specimens ; others have large female and small rudimentary male forms. 



However, I do not believe that these are the two most divergent cases in the sexual 

 relations of the genus ScalpeUum. I think there is still a third category of species in 

 this genus, viz., those which are as true hermaphrodites as other Cirripedia, and in 

 which no complemental males are developed. As a supposed species of this third 

 division I will point out Scalpelhim balanoides, Hoek. In the descriptive part of my 

 report I have communicated the fact (p. 130) that one of the specimens contained eggs, 

 though no complemental male was present at the place it ordinarily occupies. Though I 

 have studied some more specimens of this species with great care, I have not once observed 

 a male ; yet they were nearly all furnished with eggs. I then studied the body of one 

 of the specimens by the aid of transverse sections (PL IV. fig. 8, a-f) ; I found that 

 the specimen was furnished with a very largely developed testis greatly surpassing the 

 same organ in ScalpeUum vulgare. The penis of this specimen was also of considerable 



