210 MADRAS FISHERIES BULLETIN VOL. XIV, 



able to capture numbers by the simple expedient of sinking traps 

 to the bottom. He found Nautilus to be gregarious and nocturnal, 

 crawling over the bottom in troops at night time in search of the 

 crabs and molluscs on which it feeds. Figure 6l shows its 

 ordinary attitude when crawling. It is also able to swim after the 

 usual manner of Cephalopods. The earliest specimens captured 

 were taken floating or swimming on the surface. In this position 

 the numerous tentacles, 6o to 90 in number, which here take the 

 place of the arms in other cephalopods, are arranged in a radial 

 manner around the mouth and this accounts for the description 

 given of it when seen on the surface as " a shell with something 

 like a cauliflower sticking out of it." These tentacles are prehen- 

 sile and are given off from lobes of the foot surrounding the mouth. 



A dorsal lobe of the foot forms a thick and strong hood which 

 protects the whole animal when withdrawn into the great terminal 

 chamber of its shell. Unlike other cephalopods Nautilus has no 

 ink sac. 



The shell is a pretty object often thrown up on our shores during 

 the monsoon. The size is considerable, often reaching 4 to 5 inches 

 in diameter. It is a discoidal shell, coiled in one plane, and divided 

 by concave septa into a large number of chambers increasing 

 gradually in size as they approach the open terminal chamber. In 

 this the whole body of the animal is lodged. The chambers are 

 connected by a narrow siphuncle as is Spirula, and in life a narrow 

 membranous tube passes from the animal backwards through the 

 siphuncle. With increase in size, the Nautilus periodically finds 

 the body chamber too small, so lengthens and widens it in front, 

 while behind it shuts off the hinder portion of the chamber by a 

 new transverse partition. The chambers are filled with a nitro- 

 genous gas. This has value in lightening the shell and is useful 

 in adjusting the weight of the body to the particular needs 

 of the moment. It is what is known in physics as a hydrostatic 

 apparatus. 



The interior of the shell and all the septa are pearly, while the 

 outer layer is porcellanous, barred irregularly with broad reddish- 

 brown bands upon a whitish ground. 



