74 PHYSIOLOGY OF THE INVERTEBRATA., 



of an oblong pyriform shape, and secretes a brown or black 

 fluid, the colour of which is very durable. 



The Tetrabranchiata are represented by the only existing 

 genus, Nautilus, which is provided with an external chambered 

 siphunculated shell. 



Like that of the Se'pia, the mouth of the Nautilus is armed 

 with powerful jaws (Fig. 21). It leads into an oesophagus 

 which dilates into a wide crop. The crop passes into the 



Fig. 21.— Alimentary Canal of Nautilus. 



a — buccal mass, i = oesophagus, c = crop, d = stomach, e = " pyloric " 

 caecum. /= intestine, g = anus, h = so-called liver, k = funnel. 



stomach whose internally chitinous lining is thick and ridged^ 

 The caecum in Nautilus is small, and is attached to the anterior 

 portion, of the intestine. The intestine makes two abrupt 

 bends and terminates in the branchial cavity. In Nautilus 

 there are no salivary glands, unless certain small glandalar| 

 bodies within the buccal cavity possess that function. The so- 

 called liver is a racemose tetra-lobed gland, and its functioa.; 

 is, d, priori, tljat of a pancreas. 



The Tetrahranchiata have four gills and numerous short 



