MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 165 



Within the lips of each of the pericardial and renal apertures are folds from each side; they 

 are especially well developed upon the lips of the renal apertures, and lapping past each other 

 form valves winch are difficult to push aside with a probe, and which must be effectual in pre- 

 venting ingress or egress of any substance except under the control of the animal. 



The histology of the pericardial glands and the renal appendages has been investigated to a 

 limited extent by Vigelius, but our knowledge of the microscopic structure of these organs is 

 still most elementary. 



The branchial arteries run outward from the vena cava through the posterior walls of the 

 renal sacs. At about the middle of these the arteries form sinus-like enlargements, in the walls 

 of which are usually three openings — one on the posterior wall leading into the central blood 

 space of the pericardial gland, and two in the anterior wall leading into the central cavities of 

 the lobular renal appendages. 



The pericardial glands are made up of a large number of finger-like follicles radiating from 

 the central cavity, which is in communication with the branchial artery. The glands are not 

 stalked, but are attached to a quite considerable area of the wall of each renal sac around the 

 fissure leading into the central cavity of the gland. The follicles of the glands are sometimes 

 slightly constricted at their bases or may be enlarged a little distally. Blood spaces extending 

 outward in the follicles from the central cavity form a closed finely branching system. The 

 external or pericardial surface of each follicle is covered by minute pores, leading into tubules 

 which everywhere penetrate between and separate the branching blood vessels. The blood 

 vessels possess a very thin endothelial wall, which lies close to the inner side of the columnar 

 epithelium of the tubules. The structure of the pericardial glands is very similar to that of the 

 venous appendages of the Dibranchiata. 



Grobben 1 remarks upon the resemblance in essential structure of the. pericardial glands of 

 Nautilus to those of Eledone moschata. The glands are much further subdivided in Nautilus 

 than in Eledone. 



The renal appendages have much the same structure as the pericardial glands. They hang 

 in pairs from the anterior sides of the branchial arteries, pressed closely against each other so as 

 at first sight to appear like a single structure, but in reality connected only by the wall of the 

 branchial artery. 



The renal appendages are divided by narrow, not very deep, fissures into large, flattened, 

 polygonal lobes, and so present an appearance quite different from that of the pericardial glands. 

 Like the pericardial glands, the renal appendages are sessile upon the branchial arteries. 



The openings in the anterior walls of the arteries lead into a sinus-like central blood space 

 in each renal appendage. From the central blood space the branches to the lobes pass outward, 

 breaking up into numerous closed vessels. These are separated by invaginations of the columnar 

 surface epithelium, which comes into close contact with the thin endothelial walls of the blood 

 vessels. The outer ends of the tubules pushed inward from the surfaces of the lobes are radial; 

 the inner ends run irregularly. 



The renal sacs are often completely filled with a gritty substance, like fine sand. Sometimes 

 it is white, sometimes a faint rose-pink in color. This constitutes the excretory product of the 

 renal appendages. It is composed of rounded grains, formed by numerous concentric layers, 

 reminding one strongly of starch grains by their appearance. The grains are single or compound, 

 often being joined so as to form short varicose rods. Rarely irregular masses are formed. When 

 the deposit in the renal sacs is of a pink color most of the granules have a slight pink tinge. Some 

 are deep red, while others contain a deep red center and a light peripheral portion. The granules 

 are frequently found in the tubules of the appendages. 



According to Keferstein, the excreted substance found in the renal sacs contains a slight 

 amount of fat. The greater proportion is, however, made up of inorganic substances. The 

 principal of these is calcium phosphate. Lesser amounts are found of calcium sulphate, calcium 



1 Morphologische Studien liber den Harn. und Geschlechtsapparat sowie die Leibeshohle des Cephalopoden. 

 Ajo. a. d. Zool. Inst. d. Univ. Wien. T. V., 1884. 



