ANNULOSA: CRUSTACEA. 203 



extend in an opposite direction outside the visceral sac."- 

 (Owen.) 



All the BalanidcR are hermaphrodite, and this is also the 

 case with most of the Lepadida, 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 ; 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.) 



DIVISIONS OF ClRRIPEDIA. (AFTER DARWIN.) 



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 ; abdomen rudimentary, but often bearing caudal appen- 

 dages. Mouth, with labrum not capable of independent movements. 

 Larva, firstly one-eyed, with three pairs of legs ; lastly two-eyed, with six 

 pairs of legs. 



Fam. i. Balanida. 



Sessile, without a peduncle; scuta and terga (forming the oper- 

 culum) provided with depressor muscles ; the rest of the valves 

 immovably united together. 

 Fam. 2. Verrucidce. 



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



movable, but not furnished with a depressor muscle. 

 Fam. 3. Lepadidce. 



Pedunculated. Peduncle flexible, provided with muscles. Scuta 

 and terga, when present, not furnished with a depressor muscle. 

 Other valves, when present, not united into a single immovable 

 case. 



ORDER II. ABDOMINALIA. 

 Carapace flask-shaped ; body formed of one cephalic, seven thoracic, 



