462 THE ANIMAL KINGDOM. 



in Nautilus and Decapoda, close together in Octopoda. The arterial system 

 is very complete and much branched in Dibranchiata. It is said to lead 

 into true capillaries in some cases, or into coelomic sinuses in others. The 

 venous blood is collected into a large median postero-ventral vein, the vena 

 cava, which branches into four branchial arteries in Nautihis, into two in 

 Dibranchiata. These traverse the walls of the nephridial and viscero- 

 pericardial sacs on their way to the ctenidia, up which they run on their 

 ad-pallial, i.e. in Dibranchiata, fixed aspect. Each vessel is dilated in the 

 order just named, at the base of the ctenidium, into a muscular branchial 

 heart ; and before it enters the ctenidial axis, it receives veins from other 

 parts of the body. Attached to the base of each branchial heart, and 

 depending into the viscero-pericardial sac, is an appendage, the pericardial 

 gland of Grobben, or so-called fleshy appendage. It corresponds in Natitilus 

 to vascular appendages of the branchial arteries, which project into the 

 viscero-pericardial sac, and resemble the vascular tufts which project from 

 the same vessels into the nephridial sacs both of Nautilus and Dibranchiata. 

 The blood contains amoeboid corpuscles and haemocyanin. 



The viscero-pericardial sac (pericardium, secondary coelome) is of very 

 large size in JSfautilus and Decapoda. It includes the heart, the roots of the 

 branchial arteries, the branchial hearts of Decapvda, stomach, and, except in 

 the male Sepia, the genital organs as well. The testis in Sepia is contained 

 in an almost closed diverticulum of it. It communicates in Nautilus with 

 the branchial cavity by a right and left aperture close to the openings of 

 the posterior pair of nephridial sacs ; in Decapoda with the nephridial sacs 

 themselves, by a wide slit-like opening in Oegopsidae, e. g. Ommastrephes, 

 by a small pore in Myopsidae, e.g. Sepia. The corresponding sac is reduced 

 in Octopoda to a small space which incloses the pericardial gland, and opens 

 into the nephridial sac of its side by a pore ; to a narrow canal connecting 

 each space to the genital sac ; and to the genital sac itself. This series of 

 spaces is sometimes spoken of as the water-canal system. It is absent in 

 Argonauta Argo and Ocythoe tuber culata (= Tremoctopus Carenae]. 



The respiratory organs consist in Tetrabranchiata, i.e. in Nautilus, of 

 two, in Dibranchiata of a single pair, of ctenidia, free in the former, attached 

 by one aspect in the latter. The branchial artery runs up the attached or 

 in Nautilus the homologous side, the vein on the free surface. A mass of 

 cells, with intervening blood-lacunae, is situated in the line of attachment in 

 Dibranchiata. It is possibly a blood-making gland. The surfaces of the 

 ctenidia are disposed in a series of respiratory folds transverse to the ctenidial 

 axis. The folds differ in shape in Octopoda and Decapoda. 



There are four nephridial sacs in Nautilus, two in Dibranchiata, each 

 opening by its own aperture, which in Dibranchiata is often produced into 

 a papilla. The four sacs of Nautilus and the two of Octopoda are in- 

 dependent. In Decapoda they are either connected to a median sac lying 



