94 Invertebrata. 



traction of the wall of this cavity, which by driving a 

 column of water in the opposite direction with great 

 force, propels the creature by rhythmical jerks, and at 

 a rapid rate. 



On slitting open the mantle two large gills are 

 seen, one on each side, above and between which is 

 the heart-ventricle. The blood enters the gills by 

 large veins which form dilatations at the base of these 

 breathing organs, then after being aerated, it is col- 

 lected in two cavities called systemic auricles, from 

 whence it passes into the muscular ventricle which 

 drives it through the arteries into the lacunae (or tissue 

 interspaces of the body). 



Along the hinder edge of the long digestive canal 

 there is a slender tube, whose opening is also at or 

 near the mouth of the funnel, and whose upper end 

 expands into a large spongy- walled sac lying close 

 beside the liver. This sac secretes a brown or black 

 inky material which is poured out in enormous quan- 

 tities when the animal is pursued, and which by ren- 

 dering the water opaque covers the flight of the 

 cuttlefish. 



At the mouth of the mantle-cavity but not actually 

 connected with it there is a funnel, which when the 

 margin of the mantle contracts forms a narrow tubular 

 outlet for the fluid of the cavity. 



Cuttlefishes possess a brain, made up of large 

 confluent ganglia around the pharynx, and over this 

 there is a cartilaginous cover, interesting as being one 

 of the first signs of an internal skeleton, like that of 

 vertebrates in the animal kingdom. There is also a 

 large and complex eye, more like that of a vertebrate 



