114 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The nerves to the digital tentacles arise singly, as a rule, from the outer edges and lower 

 side of the pedal ganglia. (Fig. 41, 9.) Only the nerves to a few of the more dorsal tentacles 

 arise from a common nerve. (Fig. 41, 10.) The hood receives branches from several nerves. 



A small artery with thick elastic walls is found close to the inner side of the nerve. (Fig. 51, 

 A.). Just outside this is a much larger vein. (Fig. 51, V.) Both vessels are elliptical in cross 

 section. This position of the artery ami vein is so characteristic that even in extremely modified 

 cirri, such as those of the spadix, the inner side of the cirrus can be determined at once in 

 sections by the position of the vessels. 



Between the epithelium of the cirrus and the circular muscle are numerous, very large, 

 capillaries with endothelial walls. Closed capillaries are occasionally, hut rarely, found in the 

 muscular and nervous tissue. Here the circulation takes place through minute fissures in the 

 tissues. 



Immediately behind the cerebral ganglion the dorsal aorta divides into two branches — the 

 innominate arteries, from which arise branches to the eyes, buccal mass, labial tentacles, funnel, 

 shell muscles, and cephalic sheath (Text-fig. 10). The posterior portion of the hood is supplied 

 by small arteries arising directly from the innominates (10). The main branches of the innomi- 

 nates run forward and downward upon each side, giving off branches to the individual digital 

 tentacles (5, 4). 



The veins of the cephalic sheath unite in common veins which penetrate the cartilage and 

 enter the anterior end of the vena cava. 



The epithelium of the cirri forms a feature of exceeding interest. It consists of a single 

 layer of slender columnar cells. The epithelium upon the outer sides is of the ordinary type 

 and contains great numbers of goblet cells. These cells are 40/* in height by 4/< in diameter. In 

 the bottoms of the annular grooves the cells are very much shorter, often almost cubical. 



But the epithelium of the inner surface of the ridges is very peculiar. A longitudinal 

 section of a cirrus (Figs. 50 and 72) shows that the upper surface of the projecting portion of 

 each ridge is horizontal and makes a sharp angle with the inner surface, while there is a gradual 

 bend from the inner to the lower surface. The epithelial cells of the vertical inner surface are 

 exceedingly slender, having a height of 108/* and a width of 2-4/*. Their width has been exag- 

 gerated in the figures of the single cells shown at the left of Fig. 72, as well as in the main portion 

 of Fig. 72, for convenience in representation. The epithelial cells of the upper surface of the 

 projecting portion of the ridge are only about one-eighth as high and much wider, beside being 

 of a totally different character. The change from one kind of cells to the other takes place quite 

 abruptly at the sharp angle of the ridge. The change in length and character of cells is much 

 more gradual where the epithelium passes from the inner to the lower surface. The relations 

 and characters of these cells are shown as well as my limited ability as an artist allows in Fig. 

 72, which was drawn from a section stained with borax carmine and Lyons blue; the colors of 

 the stain have been copied faithfully. 



The epithelium of the upper surface contains many mucous cells the secretion of which 

 remained unstained with either stain, excepting the portion extruded from the cells and certain 

 small granules which stained red. Mucous cells are occasionally found in the depth of the 

 groove, but none, of this character at least, are found upon the inner surface of the ridge. 



The nuclei of the slender cells upon the inner face of the ridge are situated very close to the 

 bases of the cells. From the nucleus out almost every cell contains a large number of granules 

 which stain a brilliant red. Sometimes the granules are arranged in a single row extending 

 from the nucleus to the free end of the cell. Sometimes they form a dense accumulation almost 

 filling the body of the cell. A very few scattered granules were sometimes found in the base of 

 the cell beneath the nucleus, but never in any numbers or regularly arranged as the_v usually 

 were upon the outer side of the nucleus. The granules seem to be some sort of a secretory 

 product, but this is evidently of a different chemical nature, as well as physical, from that 

 formed by the cells of the upper surface of the ridge or of the entire outer sides of the cirrus. 

 Possibly its formation is connected with the function of adhesion belonging to these portions of 

 the cirrus. 



