374 Mr. Robert Garner's Malacological Notes. 



side, where the semicartilaginous rays of the long fins begin, 

 reminding us much of the similar parts in a skate. Octopus 

 has not the cups at the base of the siphon ; but it has two 

 cartilaginous styles in the sides of the mantle ; these last are 

 absent in the argonaut. The siphon in the Octopodidas has 

 not the valve which is present in the Sepiadje. This siphon 

 may be seen in the Gastropoda to arise from the body rather 

 than the mantle, and so in the Cephalopoda. 



Besides the internal skeleton the Cephalopods are furnished 

 with other new or more developed organs — their curious beak, 

 for instance, reminding us of birds or of some reptiles or 

 fishes, but, in fact, a further development of parts of other 

 mollusks similarly situated, as already alluded to. In these, 

 too, the molluscous foot is broken up or difierentiated and re- 

 solved into arms or tentacles, which are furnished with 

 peculiar suckers or hooks. We see this disintegration in some 

 Gastropods and Pteropods, and at the same time its transfer- 

 ence to the head, forming a menfum or propodium [Ampidlariay 

 Si'garetuSj Natica), or fin-like side lobes or epipodia [BuUcea). 

 Bidlcea also presents us with a tentacular lobe or super- 

 cephalic disk. With the above transposition the arms and 

 tentacles in Cephalopods are very specially developed, whether 

 as the cupuliferous arms and tentacles of ordinary species, or 

 as the less formidable sheathed tentacles of the Nautilus. 



The circulation in mollusks undergoes a progressive com- 

 plication, much as it does in the Vertebrata. They have been 

 described as being destitute of true veins ; but this is far from 

 the case, though these veins may communicate with sinuses 

 to which even the external element may have access, and such 

 cavities may be the media of absorption or nutrition rather 

 than the veins primarily. The circulation is already well pro- 

 vided for in the Lamellibranchiates, as much so in Gastropods ; 

 and it is very remarkable for its perfection in the highest 

 mollusks. These circulatory, like the other vital organs, are 

 probably originally double or bilateral, and become single by 

 development, somewhat the reverse of what is the case in 

 Vertebrata ; thus in bivalves the auricles, and less frequently 

 the ventricle, continue more or less parted, or the ventricle 

 envelops a length of the rectum, as already observed. Some 

 ArccB and Pectunculi have two hearts ; A. auricuUfera but 

 one, of the shape of an inverted M. The blood is returned 

 from the system in part directly to the heart, in part through 

 the medium of the branchiae, the latter portion also appearing 

 to have previously circulated through the renal organ ; but 

 the dibranchiate Cephalopoda are peculiar in having two auxi- 

 liary branchial hearts between the system and the branchise. 



Near the branchise, most commonly, are located the organs 



