COMPLEMENTAL MALE. 243 



part of the animal : the limbs differ greatly from those 

 both of the mature Cirripede and of the larva, but come 

 closest to the latter : the preservation of the abdomen is 

 a well-marked embryonic character. On the other hand, 

 the four rudimentary calcareous valves, the narrow orifice, 

 the hirsute outer integument, the two muscular layers, the 

 single eye, and male internal organs, are all characteristic 

 of the fully-developed condition. The four little valves, 

 as I believe, represent the scuta and terga, though they are 

 placed considerably below the orifice : the little bristly 

 points have no homological signification, and are absent 

 in the male of the following closely allied species. The 

 four pairs of limbs answer to the four posterior cirri, 

 as may be inferred from their proximity to the abdominal 

 lobe, and from the three posterior pairs closely resembling 

 each other, and differing a little from the first pair ; this 

 latter pair corresponds with the third pair in the herma- 

 phrodite form of Scalpellum. If I am right in believing 

 that only a single vesicula seminalis is ordinarily developed 

 in the male, this is a special and singular character. 



As stated in the beginning of this description, from 

 the one great fact of the absolute correspondence of the 

 prehensile antennae of the parasite, with those of the her- 

 maphrodite Scalpellum vidgare, together with its fixed 

 condition, its short existence, and exclusively male sex, I 

 have thought myself justified in provisionally considering 

 it as the Complemental Male of the Cirripede to which it 

 is attached ; but I hope final judgment will not be passed 

 on this view, until the whole case is summed up at the 

 end of the genus.* 



* I trust, before long, that some naturalist, with more skill than I pos- 

 sess, will examine these parasites on Scalpellum vulgare, which unfortunately is 

 the only species of the genus that can be easily obtained. Fresh specimens, 

 or those preserved in spirits of wine, are necessary. The action of boiling 

 caustic potash is very useful in cleaning the prehensile antennae. If these 

 latter organs are sought in the hermaphrodite for the sake of comparison, 

 young specimens, adhering to clean branches of a coralline, should be pro- 

 cured, and caustic potash used. 



