94 STUDIES IN LIFE AND SENSE. 



From the mouth-cavity leads the gullet, which may dilate to form 

 a crop in some cases (octopus, argonaut, nautilus, &c.), and which 

 terminates in the stomach. This latter, again, is usually of capacious 

 extent, and as a rule has its gullet opening in close proximity to the 

 intestinal aperture. It is besides extremely muscular. The intestine 

 is bent upon itself ; it may possess a spirally twisted portion at its 

 commencement. It is as a rule relatively short, and destitute of the 

 convolutions commonly seen in this part of the digestive tract in 

 higher animals. It terminates in the " funnel " through which, as 

 already remarked, the effete water of respiration is ejected. 



If the digestive system of any animal be legitimately described 

 as merely a tube passing through the body of the organism, such 

 a definition must likewise take account of certain lateral appendages 

 or " glands " which secrete, from the blood, fluids required for the 

 digestion of the food. Such are the salivary glands, the liver, and 

 the pancreas or sweetbread of higher animals. These glands are re- 

 presented in the cuttlefishes by organs of definite nature. Thus the 

 salivary glands open into the mouth-cavity, and number two or four. 

 The liver is proportionately large in cuttlefishes, its bile being 

 conveyed into the digestive tract by two bile-ducts, around which 

 are clustered certain structures regarded as the representatives of the 

 " sweetbread " or pancreas. The digestive system of the cuttlefishes 

 is thus seen to be of very perfect nature, and to partake of that high 

 degree of specialisation which, from their position in the molluscan 

 type, we should naturally expect their internal economy to exhibit. 



The products of digestion pass directly from the digestive system 

 into the bloodvessels. There exists in no invertebrate, any repre- 

 sentative of the absorptive system of vessels whereby the fluid which 

 is to form the blood is removed from the digestive tract and poured 

 into the blood current. But the circulation of the blood itself which 

 is colourless and, curiously enough, contains copper is carried on in 

 cuttlefishes by a well-developed system of vessels connected with a 

 central heart. The heart itself consists practically of three chambers 

 or compartments one ventricle or propelling chamber and two 

 auricles. Like every other heart, that of the cuttlefishes is a hollow 

 muscle hollow, to allow blood to pass through it, and muscular, 

 to propel the blood from its precincts. Two main bloodvessels arise 

 from the ventricle, which by its constant action is thus distributing 

 pure blood which it has received from the gills (and auricles) 

 through the body. The arteries appear to end in capillary vessels, 

 but, according to Milne Edwards, the veins possess more the cha- 

 racter of sinuses or irregular channels than of well-defined vessels. 

 By the veins, the blood, rendered impure by its circulation through 

 the body, is returned to the gills for purification. The great veins 

 carrying blood to the gills expand at the base of each gill to form two 



