CEPHALOPODA. 135 



and figure, running into one another, and separat- 

 ing, playing to and fro, contracting, and dilating, 

 appearing and disappearing with great rapidity, 

 in the most unaccountable manner. These pheno- 

 mena depend on the structure of the skin, which 

 contains elastic cavities filled with variously 

 coloured fluids, under the influence of the nervous 

 system, and therefore subject to the ever- varying 

 emotions of the animal. 



At certain times, as when alarmed, these crea- 

 tures suddenly discharge from the funnel a volume 

 of fluid, of intense blackness, which is secreted in 

 the ink-bag, a sac lying along the inferior part 

 of the body, and opening at the bottom of the 

 funnel. This fluid was used by the ancients for 

 waiting, and by the moderns in the preparation of 

 Indian-ink and sepia. 



The circulation does not differ importantly from 

 that of the Gastropoda. So far as is known, 

 there is no system of completely closed blood- 

 vessels. The blood is sometimes green or violet, 

 but sometimes colourless. Breathing is performed 

 by means of gills situated in the cavity of the 

 mantle. These organs are long pyramids, formed 

 of a central stem, beset with numerous trans- 

 verse plates or arches. It is a singular circum- 

 stance that the gills are not ciliated ; the water 

 which bathes them enters the cavity beneath the 

 borders of the mantle, and is discharged periodi- 

 cally through the funnel. 



The sexes are always distinct. In many species 

 the males are unknown ; in others, they resemble 

 the females ; but in others, they present the most 

 extraordinary peculiarities. On certain female 

 Cephalopoda there have been observed from time 



