132 THE CEPHALOPODS. 



paratus. Other portions are met with at the lower 

 part of the body, and in the fins of such as possess 

 these appendages — the calamary for example. But 

 this commencement of a skeleton must not be con- 

 founded with a corneous or calcareous structure con- 

 tained in a large cavity within the dorsal portion of 

 the mantle, and there secreted by the sides of the 

 chamber itself. In the cuttle-fish (^Sepia officiyialis) 

 this dorsal plate is calcareous, and consists of a multi- 

 tude of laminse, not closely compacted together, but 

 kept at a little distance apart, by minute, but very nu- 

 merous pillars ; the whole being a light and porous 

 mass. In the calamary (^Loligo) this plate is a long 

 horny substance, (somewhat resembling the blade of a 

 sword, or a spear head,) deposited layer by layer, and 

 increasing with the animal's growth. In both these 

 cases, the plate resembles the small lamina found in a 

 cavity of the mantle of the slug, and may be regarded 

 as a rudimentary shell ; the lingering relics of that 

 structure which is in its perfection in the lower mol- 

 lusca. In the argonaut and the nautilus, we find it 

 assuming the form and structure of a true shell, over 

 which the mantle is more or less reflected, but in which 

 the animals are housed ; the difiference between the 

 cuttle-fish and these animals being, as far as this shell 



