414 



CIRRIPEDIA. 



apodemes (n\ which leave a deep bay on the ventral surface behind the 

 peduncle. The chitinous skin of the Cirriped passes round the head 

 of this bay, but on the moult of the pupa skin taking place becomes 

 stretched out, owing to the posterior part of the larva bending dorsal- 

 wards. It is this flexure which causes the change in the position of 

 the larva. 



In addition to the remarkable external metamorphosis undergone 

 during the pupa stage, a series of hardly less considerable internal 

 changes take place, such as the atrophy of the muscles of the 

 antennae, a change in the position of the stomach, etc. 



Abdominalia. In the Alcippidae the larva leaves the egg as a Nauplius, 

 and this stage is eventually followed by a pupa stage closely resembling 

 that of the Thoracica. There are six pairs of thoracic natatory legs 

 (Darwin, No. 519). Of these only the first and the last three are preserved 

 in the adult, the first being bent forward in connection with the mouth. 

 The body moreover partially preserves its segmentation, and the mantle 

 does not secrete calcareous valves. 



The very remarkable genus Cryptophialus, the development of which is 

 described by Darwin (No. 519) in his classical memoir, is without a free 

 Nauplius stage. The embryo is at first oval but soon acquires two anterior 

 processes, apparently the first pair of antennae, and a posterior prominence, 

 the abdomen. In a later stage the abdominal prominence disappears, and 

 the antennary processes, within which the true antenna? are now visible, 



are carried more towards the ventral 

 surface. The larva next passes into 

 the free Cypris stage, during which it 

 creeps about the mantle cavity of its 

 parent. It is enveloped in a bivalve 

 shell, and the antennae have the nor- 

 mal cirriped structure. There are no 

 other true appendages, but posteriorly 

 three pairs of bristles are attached to 

 a rudimentary abdomen. Paired com- 

 pound eyes are present. During the 

 succeeding pupa stage the metamor- 

 phosis into the adult form takes place, 

 but this has not been followed out in 

 detail. 



In Kochlorine, a form discovered 

 by Noll (No. 526) and closely related 

 to Cryptophialus, the larvae found 

 within the mantle represent apparent- 

 ly two larval stages, similar to two 

 of the larval stages described by 

 Darwin. 



RhiZQCephala. The Rhizoceph- 

 ala, as might have been anticipated 

 from their close relationship to Ane- 

 lasnia sqnalicola amongst the Tho- 

 racica, undergo a development differ- 



FIG. 233. STAGES IN THE DEVELOP- 

 MENT OF THE RHIZOCEPHALA. (From 

 Huxley, after Fritz Miiller. ) 



A. Nauplius of Sacculina purpurea. 

 B. Cypris stage of Lernseodiscus por- 

 cellanas. C. Adult of Peltogaster paguri. 



II. III. IV. Two pairs of antennae 

 and mandibles; cp. carapace; a. anterior 

 end of body; b. generative aperture; c. 

 root-like processes. 



