170 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



some species of Lucina (fig. 48, a), situated on the ventral 

 margin of the mantle. In the Annelida the gills are usually 

 an appendage of the legs, and sometimes are placed directly on 

 the body or at the fore end, as in Sabella, Serpula, Terebella, 

 &c. Finally, the number of Invertebrata is by no means small 

 which dispense entirely with such distinct, conspicuous organs 



FlG. 48. -Gills of Mollusca. a, Litcina pftiUppensis, with four mantle gills behind the 

 muscle TO ; 6, Mytilns, with k the gills, and I the laminated lip ; c, Elijsia grandis 

 (Bergb.), destitute of gills ; d, Doris sp., with a tall tuft of dorsal branchiae. 



of respiration, and consequently breathe only through the skin ; 

 among the Mollusca there are the Elysiadce (fig. 48, c) and their 

 allies; among the Annelida the common leech and the Oligo- 

 chaetae (the earth-worm, <tc.); many of the lower Crustaceans 

 parasitical as well as independent all Infusoria, the Ccelente- 

 rata, and even many Echinodermata, &c. 



