A. E. Verrill — North American Cephcdopods. 339 



back of each eye-orbit. This cephalic sinus receives the blood from a 

 large vein in the median line and near the inner surface of each arm. 

 Numerous small veins from the head and eyes also enter this and the 

 ophthalmic sinuses ; others, entering the anterior vena-cava, from 

 each side, along its course, come from the muscles of the head, neck 

 and siphon, from the ink-sac, anterior part of the liver, etc. Two veins 

 of considerable size, which become sacculated posteriorly, arise from 

 the intestine and ink-sac and run back to the sacculated divisions of 

 the vena-cava. A small vein also extends along the dorsal side of 

 the efferent sperm-duct {^p). Two large pallial veins, uniting together 

 close to the branchial auricles, on each side, come from the sides of 

 the mantle (w, wc') ; one of these («c') runs from the anterior part 

 backward, and receives a branch (fig. 1) from the gill; the other (u), 

 from the middle and posterior parts forward. The posterior venae- 

 cavne (we") arise mostly in the caudal fins and posterio lateral portions 

 of the mantle ; each one receives two large branches, one anterior and 

 the other posterior, just at the point where it leaves the inner surface 

 of the mantle. From this point they run forward parallel with the 

 two posterior arteries, and converge to the region of the heart, where 

 they join the great sacculated venous vessels (r) ; along a considerable 

 portion of their course they expand and become large, elongated, fusi- 

 form organs (r'), probably renal in function, but much firmer, more 

 definite in form, and finer in structure than the more anterior renal 

 organs. 



The gills {g) are long, triquetral, acute, in section they are nearly 

 triangular, with the free ventral sides convex, and the dorsal side flat 

 or concave, except along the middle, where a thin median membrane 

 {g) arises from the central stem and unites the gill to the inner surface 

 of the mantle. The gills are composed of large numbers of thin, 

 transverse branchial laminge, which extend outward symmetrically on 

 each side from the large median blood vessels (io, Jv), each lamina 

 having a long-ovate or crescent-shaped outline. A somewhat firm 

 central axis or column gives support to the laminae and the large 

 blood vessels. The great afferent vessel (fig. 1, hv) starts from the 

 brancliial auricle {aiC) and runs along the median-dorsal side of the 

 gill, on the inner edge of the axial column; a parallel vein (fig. 1), 

 near the dorsal edge of the column, runs back and joins the lateral 

 pallial vein (yc'). Each branchial leaf receives from the afferent 

 vessel (Jy), a branch which runs along the dorsal edge, giving off at 

 regular intervals small, transverse, parallel branchlets, which in turn 

 give ofl" minute capillary vessels along their sides, and fade out near 



Trans. Conn. Acad., Vol. V. 42 June, 1881. 



