Vel 



CHAPTER I. 



MOLLUSCA.* 



Bilaterally symmetrical unseymented animals, without a locomotory 

 skeleton; with a a /if ml foot and v.si.illy a calcareous univalve or 

 It! mice shell: fit// hm'nt (supraossophageal yartyHa\circuinaxophayeal 

 i'i inj, and suboesophageal yron /> <>f yamjlia. 



SIXCE Cuvier several different groups of animals, which were placed 

 amongst the worms by Linnanis, have 

 been included in the Mollusca. Of late 

 years, however, the anatomy and de- 

 velopment of these forms have been 

 more closely examined, and it seems 

 fairly certain that some of them are 

 allied to the Worms. In any case, the 

 group Mollusca must be looked upon 



as of more limited extent than has for FIG. 492. Older larva of a Gagerqpo<2 



(after Gegenbaur). 8, Shell; P, 

 foot ; Tel, velum ; T, tentacles ; Op, 

 operculum for the closure of the 

 shell opening. 



development stand in closer relationship 



to the Bryozoa, may be removed from the Mollusca and united with 



the latter under the head Molluscoidea. The Tunicata also must 



be constituted an independent group between the Mollusca and the 



Vertebrata. 



* G. Cuvier, ' Mrmoires pour servir a 1'histoire et a I'anatoinie des Mol- 

 lusques." Paris. 1817. 



R. Leuckart, " Ueber die Morphologic mid die Verwandschaftsverhaltnisse 

 der wirbellosen Thiere." Braunschweig, 1848. 



Huxley, ' On the Morphology of the Cephalous Mollusca, as illustrated 

 by the Anatomv of certain Heteropoda and Pteropoda, etc." Pit II. Trans.* 

 1853. 



some time been the case. The bivalved 

 Brachiopoda, which in structure and 



