CIRRIPEDIA. 17 



long duration ; the animal attaches itself by the sucking disc on the antennae, while the 

 cement gland pours out a secretion which more firmly fixes the larva. The succeeding 

 moults are each accompanied with changes in structure, which, slight when considered 

 singly, in the aggregate produce important modifications in the form of the body, 

 resulting at last in the adult condition. 



Having now a general idea of the structure and growth of one cirriped we may 

 pass to a consideration of the various forms, noting their differences from the type 

 chosen. We may divide the cirripeds into four orders, APODA, ABDOMIKALIA, RHIZO- 

 CEPHALA, and THORACICA, all of which, with the exception of the Rhizocephala, are 

 treated in Mr. Darwin's masterly monograph. 



ORDER I. CIRRIPEDIA APODA. 



This group is represented by the singular genus, Proteolepas of Darwin, which 

 leads a parasitic life upon one of the higher barnacles, Alepas cornuta. Externally 

 it strongly reminds one of an insect larva fastened by two threads (the antennas) to 

 the host. All traces of the cirri are absent. The body is composed of eleven 

 segments, while the mouth is suctorial and so projects from the rest of the body as to 

 give one the impression that it constitutes a distinct segment. Inside of this proboscid- 

 iform mouth are the mandibles, which serve not only as a means of cutting the skin of 

 the host, but as hooks to anchor the parasite firmly in position. From the mouth can 

 be traced a short oesophagus, but all other portions of the alimentary tract are absent, 

 there being no stomach, no intestine, no anus. The nervous system is also apparently 

 absent, and the whole cavity of the body is occupied with the reproductive organs. The 

 antenna?, however, possesses the same structure as in the other barnacles. Of the 

 development of the single known species, Proteolepas bivincta, nothing is known. 



ORDER II. CIRRIPEDIA ABDOMINALIA. 



This order is scarcely richer in species than the preceding, but three forms belong- 

 ing to distinct genera being known, Cryptophialus of Darwin, Alcippe of Hancock, 

 and Kochlorine of Noll. The body has eleven segments, and three pairs of cirri are 

 present, but unlike all other cirripeds these are borne upon the 

 abdominal segments. The labrum or upper lip is very long and 

 capable of independent movement. The lower end of the oesophagus 

 is armed with internal teeth, reminding one of the gizzard of the 



O O 



cricket; the stomach is well developed, while the anus is at the 

 end of the last thoracic segment, just in front of the cirri. The whole 

 body is enveloped in a flask-shaped sac. It was the study of Cryp- 

 tophialus minutus (Fig. 22), which bores into the shells of Conch- 

 olepas peruviana, which first led Mr. Darwin to the study of the 

 cirripeds. This form, as its name indicates, is very small, the largest 

 being not a tenth of an inch in length. 



While in many groups of animals the females of widely different 

 families closely resemble each other, and we have to resort to the males for classificatory 

 characters, in the Cirripedia the reverse is the case, for when males exist they are always 

 of an extremely rudimentary character and always live as parasites upon the females. 

 Such is the case with the Abdominalia, where several males are attached to the mouth 



VOL. II. 2 



