170 



THE INFLUENCE OV INANIMATE SUEKOUNDINGS. 



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, Terehella, 

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

 which dispense entirely with such distinct, conspicuous organs 



Tig. 48. -Gills of Mollusca. a, ItKtna pliilippensis, with four mantle gUls belund the 

 muscle m ; b, Mytilus, with i the gills, and I the laminated lip ; e, Elyria grmdu 

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



of respiration, and consequently breathe only through the skin ; 

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

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

 chietffi (the earth-worm, &c.) ; many of the lower Crustaceans- 

 parasitical as well as independent— all Infusoria, the Coelente- 

 rata, and even many Echinodermata, &c. 



