CEMENT-GLANDS. 



461 



and is directed rectangularly outward; it is sometimes notched, and 

 even shows traces of being bifid, and bears about seven spines at the 

 end, some of which are hooked, others simple. The antennae, at first, 

 are well furnished with muscles, and serve for the purpose of walking, 

 one limb being stretched out before the other ; but their main function 

 is to attach the larva, for its final metamorphosis into a Cirriped, by 

 means of the appended disk, which can adhere even to so smooth a 

 surface as a glass tumbler*. The attachment is at first manifestly 

 voluntary, but soon becomes involuntary and permanent, being effected 

 by special and most remarkable means. 



(1189.) In each of the antennae there is situated a duct, derived from 

 a large glandular body (the cement-gland) : the termination of this 

 duct is situated in the immediate vicinity of the" adhesive disk, by the 

 assistance of which the little animal is about to fix itself permanently 

 to some foreign body and assume the Cirriped condition. 



Fig. 237. 



(1190.) Several times Mr. Darwin succeeded 

 in dissecting off the integuments of the lately- 

 attached larva, and in displaying the enclosed 

 Lepas entire, of which, in this condition, he 

 gives the following account : Whilst the young 

 Lepas is closely packed within the larva, the 

 capitulum (or shell-clad portion of the body), as 

 known by the five valves, about equals in length 

 the peduncle. The peduncle occupies the ante- 

 rior half of the larva; and even at this early 

 period the muscles of its inner tunic are quite 

 distinct. The compound eyes, as we have already 

 seen, are attached to the sternal surface of the 

 larval carapax, and are consequently cast off with 

 it : but the antennae, which are not moulted with 

 the carapax, are left cemented to the surface of 

 attachment; their muscles are converted into 

 sinewy fibres, the corium after a short time is 

 absorbed, and they are then preserved in a func- Cement-ducts 

 tionless condition. If, indeed, the peduncle even magnified. 



of an adult Cirriped be very carefully removed from the surface of 

 attachment, quite close to the end, but not at the actual apex, the 

 larval prehensile antennae can always be found, and the cement-ducts 

 traced, running in a slightly sinuous course on each side within the 

 peduncle, until they arrive at the glandular organs whence the cement 

 is furnished. Each gland contains a strongly coherent, pulpy, opake 

 cellular mass, like that in the cement-ducts ; and it is this peculiar 

 substance that constitutes the bond of union between the Cirriped and 

 the surface whereupon it becomes fixed. 



* KV. E. L. King, Annual Eeport of the E. Inst. of Cornwall, 1848. 



