CRUSTACEA ENTOMOSTRACA. 



The Cirripeds 

 were included by 

 the older natural- 

 ists in the Mol- 

 lusga,to the Lamel- 

 libranch group 

 of which the 

 bivalve shell of 

 the Lepadidae 

 with its calcareous 

 plates and the 

 siphon -like 

 peduncle give this 

 division a certain 

 external r e s e m - 

 blance. 



Their relation- 

 ship to the Crus- 

 tacea was fi r s t 

 demonstrated by 

 J. V. Thompson, 

 by the discovery 

 in the year 1829 

 of the nauplius 

 larva of Balanus. 

 The monograph of 

 the Cirripedia by 

 Charles Darwin 

 (Ray Society 

 1851-53) first 

 placed our know- 

 ledge of the struc- 

 ture of the group 

 on a satisfactory 

 basis. 



The structure 

 of the adult 



FIG. 268. a, Late nauplius, 6, metanauplius larva of Balanus 

 before the moult. Beneath the skin are the rudiments of the 

 lateral eyes (0) and all the appendages F l to F of the cypris 

 stage ; A anus ; A', A" 1st and 2nd antennae ; A' the antennae pirr.^^^ w^ll 

 with suctorial disc; D intestine; Dr gland cells of the ^ es > a 



anterior horns ; Ff frontal filament ; H frontal horns ; M df 

 mandibular foot (third pair of appendages) ; MX rudiment of 

 maxilla ; 0' unpaired eye ; 01 proboscis with mouth. (From 

 Claus.) 



as the natural 

 affinities of the 



