The Ink-bag of the Cephalopoda. — The researches of M. 

 Paul Girod upon a great number of Cephalopods of the North 

 sea and the Mediterranean, researches carried on in several suc- 

 cessive sojourns at Roscoff and Banyuls, have elucidated many 

 points in the anatomy, physiology and development of the ink- 

 bag of those mollusks. The ink-bag is a long, black, pyriform 

 sac opening at the summit of a papilla upon the posterior lip of 

 the anus, and consists of a large reservoir, and of an ink-gland 

 attached to the posterior face of the reservoir, and communicating 

 with it by means of a small round orifice at its upper part. This 

 description differs from that of preceding naturalists, whose state- 

 ments are to the effect that the secretory apparatus consists of a • 

 reservoir whose walls are thrown into folds circumscribing spaces 

 which pour the products of secretion directly into it. In the 

 decapods the gland is free and projects into the ink-sac, but in 

 the octopods the walls of the glands are united for much of their 

 extent with the wall of the reservoir. 



Ink-sac and gland are enclosed in a common envelope, consist- 

 ing of an external tunic of conjunctive tissue; a middle tunic 

 composed of a bed of smooth transverse muscular fibers crossed 

 by a layer of horizontal fibers, and succeeded by a layer of pig- 

 ment cells ; and an internal tunic constituting the special mem- 

 branes of the gland and reservoir. At the mouth of the sac is a 

 terminal ampulla, bounded at each end by a thickening of the 

 conjunctive tissue of the wall of the sac with a corresponding 

 ring of muscular fibers from the transverse layer, thus forming a 

 double sphincter. 



The ink-sac is lined with pigmented pavement epithelium, ex- 

 cept the terminal ampulla, which is lined with cylindrical epithel- 

 ium similar to that of the epidermis of cephalopods. 



The gland is composed of undulating lamellae, leaving between 

 them spaces of variable form. These lamellae, flat near the orifice 

 of the gland, become concave as they recede from it, and thus 

 form concentric cups enveloping a central whitish mass (forma- 

 tive zone), and becoming of a more vivid black as they are more 

 distant from the center. Analysis of the black secretion proves 

 it to consist of 60 parts of water, 30.5 parts of organic insolu- 

 ble matters, a little less than one part of soluble organic mat- 

 ters, and 8.6 parts of soluble and insoluble mineral substances. 

 Among the soluble inorganic matters are carbonic acid and the 

 sulphates and chlorides of sodium, potassium, magnesium and 

 lime, while among the insoluble matters are carbonate of lime, 

 magnesia and peroxide of iron. Iron and copper are both pres- 

 ent in the blood of the Cephalopoda, the latter metal as a com- 

 ponent of hemocyanine, which plays in these creatures the role of 

 hemoglobine in vertebrates. In the soluble organic matters 

 neither urine, uric acid, xanthine nor guanine can be detected, so 

 that the gland is proved not to be a depuratory urinary organ. 



