CEPHALOPODA. 

 214 



579 



Nautilus Pompilius. 



creases in thickness, becomes more muscular, and extends freely out- 

 wards, forming a wide concave fold on the dorsal aspect (e), which is 

 reflected over the black-stained involuted convexity of the shell. The 

 margin or collar of the mantle is continued downwards and forwards 

 on each side with a sinuous outline, and is perforated below for the 

 passage of the muscular expiratory and excretory tube called the 

 funnel (i). Besides the muscularity of the free border of the mantle, 

 which indicates its power of extension and contraction, its surface is 

 studded with the orifices of many minute glandular crypts ; and it is 

 the organ by which the growth of the shell is principally effected. 

 The nidamental glands form, in the female, two circular convexities 

 on the ventral surface of the abdomen, behind which the mantle is 

 encircled by a thin layer of brown matter, like the periostracum, 

 which band is very narrow above and below, but expands on each 

 side into a broad plate, corresponding in size and form with the 

 surfaces of attachment of the two great muscles for adhesion to the 

 shell. 



The anterior or muscular division of the Nautilus, which may be 

 termed the head, forms a strong and wide sheath, containing the 

 mouth and its more immediate appendages ; its inner surface is for 

 the most part smooth, the outer one divided and extended into many 

 parts or processes. The chief of these forms a broad triangular mus- 

 cular plate or hood (/), covering the upper part of the head, and 

 presenting a middle and two lateral superficies ; the former being 



