96 



COMPARATIVE ANATOMY 



CHAP. 



D. Cephalopoda. 



The gills of the Cephalopoda are always feathered on both sides. Those of the 

 Dibranchia have been the most thoroughly investigated. In Sepia, each gill has 

 the shape of a slender cone, its whole length being applied to the visceral dome in 

 the mantle cavity, in such a way that the base is directed dorsally towards the apex 



of the visceral dome, and the point ventrally 

 towards the free edge of the mantle fold or 

 the mantle cleft (Fig. 80, p. 83). The 

 points of the two gills diverge. 



The two rows of flat triangular branchial 

 leaflets (Fig. 92) are carried by the two 

 branchial vessels, each leaflet being attached 

 by one end of its base to the branchial artery 

 arid by the other to the branchial vein. In 

 the axis of the gill between the two vessels, 

 and also between the bases of the two rows 

 of leaflets, a channel is formed which com- 

 municates by a slit between each successive 

 pair of leaflets with the mantle cavity ; 

 through this canal the respiratory water 

 freely flows. The slits in this axial channel 

 are arranged alternately on each side, like 

 the leaflets between whose bases they lie. 

 The branchial vein forms the posterior sup- 

 port of the gill turned towards the mantle, 

 and the branchial artery the anterior support 

 turned towards the visceral dome. The 

 artery is united along its entire length with 

 the integument of the visceral dome by a 

 membrane of connective tissue. The an- 



" blood-making gland" (9), through which 

 venous blood flows ; 10, 11, vessels carrying 

 the venous blood which has passed through 



FIG. 92. Diagram to illustrate the struc 

 ture of the gill of Sepia (after Joubin). 1, 

 Branchial vein (containing arterial blood) ; 2, 

 branchial canal ; 3, branchial] artery (contain- 

 ing venous blood); 4, special branchial vein 

 (vas efferens)of each leaflet ; 5, special branchial 

 artery (vas afferens) of each leaflet ; 0, suspensor 

 of the gill, which attaches the branchial artery 1 

 (3) to the posterior integument of the visceral terlor ed S e of each leaflet ( that facm g tlie 

 dome (12) ; 7, suspensor of each leaflet to the visceral dome) is connected with this mem- 

 general suspensor (6) ; 8, one of the connecting brane, which may be called the gill-suspen- 

 vessels between the branchial artery and the 8Qr> by meang of another triangular mem- 

 brane. A special vein runs along the 

 posterior free edge of each leaflet, and enters 

 the "blood-making" gland back to the venous the general branchial vein at its base ; and 

 sinus at the base of the gill. The arrows in- a spec i a i arte ry runs along the anterior edge, 

 dicate the direction of the blood-stream. . , , c , f -, a , -. . -, 



i.e. along that edge of the leaflet which is 



fastened to the suspensor. Each leaflet is wrinkled in such a way that the folds 

 on the two surfaces alternate, each fold being creased in its turn. These two systems 

 of folds cross each other at right angles, and serve to increase the respiratory surface. 

 At the point where the suspensor of the gill passes into the integument of the 

 visceral dome, it contains a cellular body, which is traversed by a system of inter- 

 cellular blood-channels. This may perhaps be a blood-making gland. It receives 

 venous blood from branches of the principal branchial artery and of the special 

 arteries of the leaflets, and returns the same along two veins which run back to the 

 base of the gill, there, with others, to open into the venous sinus of the renal organ ; 

 from this organ the blood passes for the second time along the branchial artery into 

 the gill. We thus find that not all the venous blood which is conducted by the 

 branchial artery towards the gills enters the leaflets for purposes of respiration ; part 



