MOLLUSC A. 



59 



hold it down to the mouth for the beaks to tear and 

 cut up at their pleasure. 



The breathing organs are gills exposed to the water 

 in the mantle cavity, into which opens the intestine 

 and the peculiar gland known as the ink bag, and the 

 generative organs. 



The nervous ganglia are very highly organized ; and, 

 though they are strictly molluscan in general structure, 

 have a brain case, or sort of cartilaginous skull,* which 

 has been erroneously compared with that of a verte- 

 brate. The eyes are huge, in comparison with tlie 

 head, and perfect, set in remarkably deep sockets, and 

 have in some species eyelids. Near the upper end (<?>'') 

 is an opening, supposed to be for the excretion of tears, 

 or some sort of lubricator for the surface of the eyes ; 

 and in the figure this is accompanied by a notch like 

 the lacrymal sinus in vertebrates. Below the eye is a 

 pit, very small in the species figured (Ommastrephes), 

 and hidden by the mantle, but in others quite large, 

 and plainly visible, supposed to be an organ of smell. 

 In Octopus, the devil-fish, and in Nautilus, this hollow 

 is capped by a sort of short tentacle or fleshy tube. 

 The ear is internal, and situated in the brain case, on 

 the lower ganglia, but has not been proved to connect 

 with the exterior, though there is a partial canal like 

 the inner part of an external ear. 



The Squid, or arrow-fish, is common on our shores. 

 Their mode of progression is backwards towards the 

 hindmost or pointed end, instead of the head, — a most 



* These and many other forms can be obtained from fisher- 

 men. Mr. Vina! Edwards, of Woods Holl, Mass., deals in these 

 and other animals for the use of naturalists. 



