ANNULOSA: CEUSTACEA. 181 



rents of water, and thus bringing food to the animal. There 

 are no specialised respiratory organs in the family of the 

 BalanidcB. 



In the Barnacles (Lepadidce, fig. 50, 5) the anterior ex- 

 tremity of the animal is enormously elongated, forming with 

 the prehensile antennae, the cement-ducts, and their exuda- 

 tion, a long stalk or peduncle, whereby the animal is attached 

 to some solid object. At its free extremity the peduncle bears 

 the 'capitulum,' which corresponds to the shell of the Ba- 

 lanoids, and is composed of various calcareous plates, united 

 together by a membrane, moved upon one another by appro- 

 priate muscles, and protecting in their interior the body of the 

 animal with its appendages. The thorax and limbs resemble 

 those of the Balanus-, but 'slender appendages, which from 

 their position and connections are homologous with the 

 branchiae of the higher Crustacea, are attached to, or near to, 

 the bases of a greater or less number of the thoracic feet, and 

 extend in an opposite direction outside the visceral sac.' 

 (Owen.) 



All the Balanidce are hermaphrodite, and this is also the 

 case with most of the Lepadidce, but some extraordinary 

 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 antenna?, 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 

 vulgar e 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.) 



