CEPHALOPODA. 325 



Tliere are several small intervals left between the muscular fibres and 

 corresponding round apertures (i) in the membrane of the vein and 

 peritoneum. This communication, with tlie general abdominal cavitj', 

 is similar to that already noticed in the Aplysia*: M.Valenciennes* 

 detected the same structure in the specimen of the Nautilus dissected 

 by him.f 



The branchial circulation may be considered to commence, when 

 the blood again begins to move from trunk to branches, four of 

 which are continued from the terminal venous sinus to convey the 

 carbonized blood to the four gills, of which there is a larger (and a 

 smaller one) on each side. Each pair of gills is connected by a 

 common peduncle to the inner surface of the mantle ; the larger 

 branchia consists of a central stem supporting forty-eight vascular 

 plicated lamellae on each side ; the smaller branchia has thirty-six 

 similar lamellee on each side. 



The four vessels(^y) continued from the venous sinus have attached 

 to them, in their course to the gills, clusters of glandular follicles 

 (jf, g) of a simple pyriform figui'e : each vessel has three clusters of 

 such glands contained in the membranous receptacles above men- 

 tioned. The walls of these receptacles exhibit in some parts a fibrous 

 texture, apparently for the purpose of compressing the follicles, and 

 discharging the contents of the membranous receptacles into the 

 branchial cavity, by the apertures above mentioned at the base of the 

 gills. Doubtless, therefore, the glands are emunctories, and eliminate 

 from the venous blood an excretion, most probably analogous to 

 urine. Their analogues exist in the higher Cephalopoda, in which 

 they are considered to act as kidneys by Mayer ; and it is more 

 philosophical to conclude that the organs of so important an excretion 

 should be present in all the class, than that they should be represented 

 by the ink-gland and bag, which are peculiar to one order. 



The veins (f,f) extend beyond the follicles each to the root of its re- 

 spective gill, where it receives a small vein. At this part there is a valve 

 (/i) which opposes the retrogression of the blood ; the vessel, which may 

 now be termed branchial artery, penetrates the root of the gill (i), and 

 dilates into a Avider canal, which is continued through the soft white 

 substance forming the branchial stem. A double series of branches 

 are sent off" from the lateral lamellse, which ramify and subdivide to 

 form the capillary plexus, from which the returning vessels terminate 

 in the branchial vein. These veins (/, /) quit the roots of the gills, 

 and return to terminate at the four corners of a subquadrate trans- 

 versely elongated ventricle (m). From this ventricle two arteries 

 arise, one superior and small (n), the other inferior (r), and strength- 



* P. 301. t Loc. cit. p. 287. 



Y 3 



