SEXUAL RELATIONS. 25 



scuta and two terga of ordinary Cirripedes ; and between the 

 scuta a minute black eye is generally conspicuous. In 

 S. ornatum the beads, I may remark, on the two sides are 

 not equal ; those either on the right or on the left side, 

 being larger than those on the opposite side, so that the 

 animal externally is asymmetrical. Inside, within a tubular 

 sack, the thorax is lodged, supporting four (instead of six) pairs 

 of limbs; and these, instead of forming biramous, multiarti- 

 culated, captorial cirri, are reduced to almost a rudiment, sup- 

 porting a few long sharp spines, which apparently act only as 

 defensive organs. At the end of the thorax there is seated a 

 large abdominal lobe, which does not occur in the other 

 sex. Hence the thorax, though rudimental, has been spe- 

 cially modified. Of the mouth and stomach there is not 

 a vestige. Constructed as these males are, assuredly they 

 have no claim to be ranked amongst the Lepadidse or 

 pedunculated Cirripedes ; nor is it possible to class them in 

 any group whatever of ordinary Cirripedes. In 8. vulgare 

 the males are attached, often several together, to the extreme 

 edges of the two scuta, and therefore immediately over the 

 orifice leading into the sack; in S. rutilum and ornatum^ they 

 are attached in concavities on the under side of both scuta, 

 just above the depression for the adductor scutorum muscle. 

 In the former of these species, the pit for the reception of the 

 male is formed by shelly matter not having been deposited 

 over a certain space on the under side of the valve; and 

 the pit is converted by a covering of membrane into a 

 pouch. As there are two scuta so there are two pouches, 

 in each of which a male is lodged ; hence, according to the 

 Linnean nomenclature, Scalpellum ornatum may be said to 

 belong to Diandria monogynia. As these males, from 

 being mouthless, soon die, they are succeeded by successive 

 pairs; the pupa being led by a wonderful instinct to crawl 

 into the pouch, and there undergo its metamorphosis. 



Lastly, the males of Alcippe and Cryptophialus (PL 23, 

 fig. 19, and PL 24, fig. 19) are remarkable for their simi- 

 larity to each other, considering the essential dissimilarity 

 of the two females. The females live in cavities which 

 they excavate in the shells of Molluscs, and within which 

 they are attached by a horny disc ; this disc is the only part 



