VII 



MOLLUSCATHE ALIMENTARY CANAL 



197 



which serves as reservoir and duct for the pigment. The latter, after being formed 

 in the gland, passes through an 

 aperture in its wall into this 

 reservoir. The cavity of the 

 gland is traversed by numerous 

 perforated and richly vascular- //3 



ised lamella? of connective 5- 



tissue, which are inter - con- 

 nected in such a way as to form 

 a kind of sponge-like structure. 

 Xew lamella? are continually 

 being put forth by the formative 

 zone of the gland, which is a 

 narrowed portion bent back 

 downwards, while the oldest 

 lamella?, which lie nearest the 

 aperture of the gland, become 

 detached and degenerate. All 

 the lamella? are covered by a 

 glandular epithelium and the 

 formation of the pigment can 

 be traced in all its stages from 

 its appearance in the epithelial 

 cells of the formative zone to 

 its condition in those of the 

 oldest lamella?. In the forma- 

 tive zone, the young glandular 

 cells are at first colourless. In 

 the succeeding lamella?, how- 

 ever, pigment granules increase 

 in number and from the older 

 lamella? are emptied into the 

 cavity of the gland, the epi- FIG. 167. Morphology of the pigment gland (ink-bag) of 

 thelial cells then becoming the Cephalopoda (after P. Girod). A, Median longitudinal 

 j i 1 section through the ink -bag of an adult, n, Anus ; 1, terminal 



detached and breaking up. ^^ common to the rec tum (-2) and the duct of the ink- 



Both the gland and the reser- bag ; 3, ampulla ; 4 and 5, sphincter muscles of the ampulla ; 

 voir are surrounded by a vascul- 0, duct of the ink-bag ; 7, pigment reservoir ; 8, opening of 

 arised integument of connective the Pigment gland into the reservoir ; 9, portion of the gland 

 . . , , . , , traversed bv lamellae ; 10, formative zone of the lamellae, 



tissue ; the same integument B Q Varioug stageg in the development of tne pigm ent 



forms the framework of con- gland ; B, anal papilla ; 0, invagination in the same ; D, ap- 



nective tissue running through pearance of two new depressions at the base of C; these 



the lamella? or trabecula? within increase in depth, the one becoming the pigment gland b, the 



,1 -I other the rectum 2. In F, the formative zone has appeared 



in the gland, in G, the first lamellae and the duct. H, I, K, 



The ink-bag is further envel- ehanges i u the relative positions of the rectum and gland in 



oped as a whole in a tough integu- the course of development, seen from the posterior (mantle) 



ment consisting of three layers si(le - In H > the rectum lies behind the ink-bag. In I, the 



(1) an inner glittering silvery latter has * hifted ' and in K lies behind the rectuin (on the 



, J mantle side), 

 layer (argentea), similar to the 



corresponding layer in the outer integument ; (2) a central muscle layer (inner 

 longitudinal and outer circular muscles ; and (3) an external layer of connective 

 tissue. 



The terminal ampulla has, at its two narrow ends, folds projecting inward and 

 functioning as valves ; it can be closed at these parts by sphincter muscles. The 



