ANNULOSA: CRUSTACEA. 2QI 



exceptions occur in this latter order. Thus, in some species 

 of Scalpellum the individual forming the ordinary shell is 

 female, and each female has two males lodged in transverse 

 depressions within the shell. These males " are very singular 

 bodies; they are sac-formed, with four bead-like rudimental 

 valves at their upper ends ; they have a conspicuous internal 

 eye ; they are absolutely destitute of a mouth, or stomach, or 

 anus; the cirri are rudimental and furnished with straight 

 spines, serving apparently to protect the entrance of the sac ; 

 the whole animal is attached like the ordinary Cirripede, first 

 by the prehensile antennae, and afterwards by the cementing 

 substance. The whole animal may be said to consist of one 

 great sperm-receptacle, charged with spermatozoa; as soon as 

 these are discharged, the animal dies." 



"A far more singular fact remains to be told; Scalpellum 

 vulgare is, like ordinary Cirripedes, hermaphrodite, but the 

 male organs are somewhat less developed than is usual ; and 

 as if in compensation, several short-lived males are almost 

 invariably attached to the occludent margin of both scuta. 

 ... I have called these beings complemental males, to signify 

 that they are complemental to an hermaphrodite, and that 

 they do not pair like ordinary males with simple females" 

 (Darwin). 



As regards their distribution, the Balanoids are shallow- 

 water forms, and Balanus itself is cosmopolitan in its range, 

 though, geologically, quite a modern genus. The Lepadoids 

 are not only found attached to floating bodies, dead or alive, 

 but also extend to great depths. Scalpellum, which is a com- 

 mon Cretaceous genus, goes down to 3000 fathoms. Alcippe 

 (which is without a shell and has only three pairs of feet), 

 bores holes in the shells of Gasteropods. 



DIVISIONS OF CIRRIPEDIA. (AFTER DARWIN.) 



SUB-ORDER I. THORACICA. 



Carapace, either a capitulum on a pedicle, or an operculated shell with 

 a basis. Body, formed of six thoracic segments, generally furnished with 

 six pairs of limbs j abdomen rudimentary, but often bearing caudal appen- 

 iges. 



Fam. i. Balanidce. 



Sessile, without a peduncle ; scuta and terga (forming the operculum) 

 provided with depressor muscles ; the rest of the valves immov- 

 ably united together. 

 Fam. 2. Verrucidce. 



Sessile. Shell asymmetrical, with scuta and terga, which are mov- 

 able, but not furnished with a depressor muscle. 

 Fam. 3. Lepadidcf. 



Pedunculated. Peduncle flexible, provided with muscles. Scuta 



