114 



THE CRUSTACEA 



shell to the substratum (Fig. 64, ant, Fig. 67, A'). They appear, 



however, to be absent in the Acrothoracica. 



The antennae disappear in the adult in all normal Cirripedia. 



Their possible persistence in the Ascothoracica will be referred to 



later. 



The month-parts consist of simply formed mandibles, maxillulae, 



and maxillae, the last united at the base to form a lower lip. The 



upper lip is large, often bullate, and at the sides, between it and 



the mandibles, are a pair of setose 

 lobes which have been sometimes in- 

 terpreted as lateral lobes of the labrum, 

 but which seem undoubtedly to be the 

 mandibular pal^js. 



The appendages of the " thoracic " 

 region, of which there are normally 

 six pairs, form the characteristic "cirri" 

 from which the name of the oixler is 

 derived (Fig. 67, Of). Each consists of 

 a two -segmented protopodite bearing 

 two long multiarticulate rami, the seg- 

 ^^ ments of Avhich are fringed with long 

 hairs forming, when the cirri are pro- 

 truded from the orifice of the shell, a 

 "casting-net" for the capture of prey. 

 The cirri increase in length and in the 

 number of segments in the rami from 

 before backwards, and the number of 

 segments also increases with the age 

 of the animal. The fii'st pair are com- 

 monly, at least in the Pedunculata, 

 Dissection of Lepas from the side. Separated by a little spacc from the 



^', antennule ; C, carina ; C(«, cement- fnllnwino- mirs: nnrl mnrp plnsplv 

 gland and duct; Cf, cirri (thoracic lOllOWUlg paUS, anCl mOlC ClOSCJy 



appendages) ; L, hepatic caeca ; M, associated with the mOUth - parts, 

 adductor muscle ; Od, oviduct ; Ov, _, i /> in 



ovary; P, penis; Sc, scutum; T, 1 Urthcr, the hrst twO Or the first 



frrom^cSus^riLTftiog''^"'''™- three pairs are _ distinguished from 



the posterior pairs by being shorter 

 and by having the segments beset with stiff spines which prob- 

 ably aid in the prehension of food. In the parasitic Anelasma the 

 cirri are short, obscurely segmented, and quite devoid of setae 

 (Fig. 68). 



In the Acrothoracica the cirri are reduced in number by the 

 disappearance of the second and sometimes also of the third pair, 

 and the first is separated by a wide space from the remaining pairs, 

 which are crowded together at the posterior end of the l)ody. The 

 first pair are reduced to small papillae in Crjipiophialus, l)ut in the 

 remaining genera they are closely approximated to the mouth-parts. 



Fig. 67. 



