232 MANUAL OF ZOOLOGY. 



scuta and terga (forming the operculum), though movable, are 

 not furnished with a depressor muscle. 



In the Barnacles (Lfpadida, fig. 86, b] the anterior extremity 

 of the animal is enormously elongated, forming with the pre- 

 hensile antennae, the cement-ducts, and their exudation, a long 

 stalk or peduncle, whereby the animal is attached to some solid 

 object. The peduncle is cylindrical, of varying length, flexible, 

 and furnished with proper muscles. In some species it is naked, 

 but in others it is furnished with calcareous scales. At its free 

 extremitythe peduncle bears the "capitulum," which corresponds 

 to the shell of the Balanoids, and is composed of various cal- 

 careous plates, united together by a membrane, moved upon 

 one another by appropriate muscles, and protecting in their 

 interior the body of the animal with its appendages. The 

 thorax and limbs resemble those of the B alarms ; 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 Balanida are hermaphrodite, and this is also the 

 case with most of the Lepadidcz, 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 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 ; Scalpelhim 

 vulgare is, like ordinary Cirripedes, hermaphrodite, but the 

 male organs are somewhat less developed than is usual ; and, 

 as if in compensation, several shortlived 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), 



