BIVALVES — THEIR DIGESTIVE ORGANS. 301 



does not pass through the heart ; and in the Anomia the 

 heart lies upon the intestine. In the Ungulina, Duvernoy 

 finds that the gut passes not through the cavity, but through 

 the parietes of the heart, — a fact which militates against 

 the hypothesis that this curious penetration of the heart in 

 these mollusks is to render easy a more immediate passage 

 of the chyle into the circulating system. His own less pro- 

 bable conjecture is, that the contractions of the heart may 

 aid the action of the intestines : " II m'a semble plus exact 

 d'attribuer ce singulier rapprochement a la necessite d'exciter 

 et d'aider les contractions de l'intestin pour la defecation." * 

 In this slight sketch I have purposely omitted to notice 

 a very remarkable organ connected with digestion, and called 

 the crystalline stylet. There is attached to or near the 

 stomach a small process which Deshayes compares to the 

 vermiform process of the coecum in the higher animals. It 

 is filled with this stylet, — an elastic, transparent, firmly gela- 

 tinous cylinder, rounded at one end and pointed at the 

 other. The anterior extremity of this body is attached to 

 the parietes of the stomach by means of small extremely 

 thin and irregular auricular processes, while the other end 

 projects into the stomach. The use of the organ is, per- 

 haps, still conjectural. Lister, and the anatomists of his 

 time, sometimes speak of it as analogous to the spine of 

 vertebrated animals, and sometimes as connected with the 

 reproductive function. Poli believed that it served to shut 

 up the pores by which the bile is admitted, and so to regu- 

 late the flow of that secretion into the stomach. Blainville 

 confessed his entire ignorance of its function ; and Deshayes 

 hesitates to suggest that it may act in bruising or com- 

 minuting the food. Mr. Garner asserts it to be " evi- 

 dently analogous to the tongue of the Patella and other 

 cephalous mollusca." Like the tongue, it is secreted 

 from behind, and comes forward into the stomach ; and the 

 auricular processes or membrane is analogous to the mem- 

 brane always found at the end of the tongue in other mol- 

 lusca. Mr. Garner's opinion of its use, therefore, seems to 

 be the same as Deshayes, but, he says, it has another use 

 assigned to it, — " the giving elasticity to the foot, or, in the 

 Anomia, where its extremity is seen in the mantle, the pre- 

 serving in its situation the free extremity of the left lobe 

 of the latter part." It may lessen the credit due from us 

 to Mr. Garner's ingenious analogy, to remember that the 

 stylet is not exclusively confined to these tongueless 



* Ann. dcs Sc. Nat. (1842) xviii. US. 





