82 



MOLLUSCOIDEA. 



sisting of calcareous processes of the dorsal valve of the shell (fig. 

 555). They have the form of long appendages rolled up in a conical 

 spiral on the anterior side of the body ; and they are traversed, as 

 are the labial palps of many Lamellibranchs, by a groove. The edges 

 of the groove give rise to close-set and long fringes composed of stiff 



jj 



St' 



FIG. 556. Development of Argiope (after Kowalevski). a, Larva, the gastric cavity of which 

 has given rise to the diverticula of the body cavity (Lh); D, gut. b, Larva with three 

 regions or segments, c, Larva with four bundles of setae in the mantle-lobes of the middle 

 segment, d, Later stage, e, Attached larva with mantle lobes bent anteriorly, f, The 

 tentacles (T) are developed ; St, peduncle. 



and movable filaments, the ciliated covering of which produces a 

 strong current which leads small particles of food to the mouth 

 opening. 



The heart is placed on the dorsal side of the anterior part of the 

 intestine (stomach). It receives the blood through a venous trunk 



