OR USTACEA— OUTER ORGANISA TION 



303 



The simOarity to Crustaceans in outer appearance is only retained in the free-moving 

 young stages, while in the adult forms this similarity is hardly recognisable. If we 

 first consider the attached Lepadidce (Figs. 204 and 205), we can distinguish out- 

 wardly an attached peduncle and a flattened shell, with a slit-like aperture on one side 

 carried by the peduncle ; this shell consists (in Lepas) of 5 calcareous plates. If we 

 open the shell we find within it the indistinctly segmented body, which carries 

 long tendril-like feet (Fig. 205) and is attached to the shell near the point of inser- 

 tion of the peduncle. The tendril-like feet are found on that side of the body turned 

 away from the peduncle. A thorough ontogenetic and anatomical study of Lepas 

 has now proved that these parts are to be described as follows. The peduncle 





Fig. 204.— Lepas ana- 

 tifera after Darwin. 

 Seen somewhat diagon- 

 ally from the carinal side, 

 c, Carina ; t, tergum ; 9, 

 scutum ; ^, peduncle. 



a' 



Fig. 205. — Organisation of Lepas, after 

 Glaus. The right half of the fold of the 

 hody integument with its calcareous plates 

 removed, t, Tergum ; s, scutum ; c, carina ; 

 m, closing muscle of the scuta ; i, liver ; 

 od, oviduct ; ov, ovarium ; cd, cement 

 glands ; a^, anterior (adhering) antenna ; (, 

 testes ; vd, vas deferens ; p, cirrus-shaped 

 penis. 



corresponds with the prolonged anterior portion of the Crustacean head, which has 

 become attached, and which still carries on its anterior end the much-simplified 

 anterior antennse in the shape of very small adhering organs (Fig. 205, aPj. The shell 

 is an integumental fold arising from the posterior head region. It answers to the 

 shell or shield of other Crustaceans. In the chitinous integument of this fold in the 

 Cirrepedia, however, there arise by calcification the various calcareous plates, to 

 which we shall again refer. The part of the indistinctly segmented body enclosed 

 by the shell which lies anteriorly next the peduncle con-esponds with the posterior 

 head region, while the remainder, which carries the tendril-like feet, answers to the 

 thorax of an JSntomostracan ; and in addition to these parts there is a small trun- 

 cated portion representing a reduced abdomen. The abdomen carries a long 



