104 



INVEIiTEBKATE ANIMALS. 



The iiuier surface of the valves of the shell is lined by expansions 

 of the iutegTinient, which are called the " niautle-lobes," and which 

 secrete the shell. The cligestive organs and muscles occupy a small 

 space near the apex or "beak" of the shell, which is partitioned off 

 by a membranous ])artition, perforated b}' the ai:ierture of the mouth. 

 The remainder of the caA'ity of the shell is almost filled by two long 

 processes, deiived from the sides of tlje moutli, fringed with lateral 



Fig. iXi. — T,'rcbmt«lii {U'ulilheimia I Jlai\'Xrns. A, Tiie sin 11 viewed IVniii licliiiirl, 

 sliowiiig the drjrs;il ^alve, and tlie iierforated suniniit of tin' ventral \al\'i' aliove it. 

 B, Inner view of tlie dorsal \'al\'e, showing the shelly loDp (?) wliicli stijiports the 

 spiral arms. C, Inner ^iew of the venti'al valve, showing the foramen or ajierture 

 (/) in the Ijeal;, thi-ough whieh the niusenlar stalk of attaehment passes. D, 

 J^ongitndiiial ami vertieal si'etion of the animal, showin.i^ the sjiival arms (c), the 

 stcniiaeh (s), and the liver (*). At / i,'' the (j|iening in the heak, with the .stalk of 

 attaehnn-nt (,.) jiassing thrniigh it. (After Davidson and Owen.) Some details 

 have Ijeeu omitted in ligs. B, C, and D, for the sake of elearni ss. 



branches, and termed the "arms" ('fig. '{?,!'), 1)\ These arms are 

 usually closely coiled up, and serve to olitain food for the animal. 

 It is freim these organs that the name of the class is derived (Gr. 

 hnii:/iiiiii, arm ; and piuji'x, feet). The arms also seive as res])iratory 

 org.-ms, and in many forms they are .stipported on an internal calca- 

 reous framesvorii or skeleton, sometimes called the "carriage-spring 

 api.ai.'ilns," 



