168 IMEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



to pass through the opening directly upon the surface of the gonad without at any point passing 

 freely aiToss the ccelom. The area of attachment of the gonad to the pallio-visceral ligament 

 is quite wide. 



At the aperture of the gonad the ocelomic epithelium is continued inside the ciivity of the 

 gonad. Thus the cavity of the ovary or of the testis is a nearly inclosed portion of the ccelom. 

 The ova and follicle cells are developed from the cceloniic epithelium. 



The genital ligament is raised from the upper or anterior surface of the gonad along two 

 lines. (Figs. 38 and 39.) The right elevation forms a fold which incloses and suspends the second 

 loop of the intestine. As the sides of the fold come together l)etween the two parts of the loop 

 a mesentei'v is formed binding these together. The anteriorly directed portion of the loop lies 

 next the gonad. As this passes ])eyond the gonad anteriorly into the rectum it remains inclosed 

 by the fold, which is here produced directly from the portion of the pallio-visceral ligament 

 between the two anterior viscero-pericardial openings. 



The second elevation of the genital ligament runs to the left side of the gonad and is pro- 

 duced from hei'e to the posterior portion of the stomach as a distinct ligament. 



The upper end of the genital ligament is sometimes found to be thickened antl shrunken, 

 appearing as if it contained muscular tissue and had contracted strongly. 



Although the second loop of the intestine and the stomach appear to lie in the ccelom, they 

 are in reality outside of it. They lie in pockets of the hsemociBlic membrane, which is only 

 more closely applied to these organs than to the lobes of the li\(M'. In the case of the stomach 

 this is quite evident. With the intestine it is less so, but examination shows that the ligament 

 surrounding the second loop of the intestine is continuous with the hicmoctelic membrane 

 around and between the two branches of the loop. 



In fact, these ligaments are composed of double lamellse containing the viscera inside them, 

 and covered outside by the crelomic epithelium. They have something the same relation to the 

 ccelom as the mesenteries of a vertebrate. The blood sinuses contained by them may 1)e con- 

 sidered as portions of the hsemoccel. The ligament of the .stomach is sometimes jdainly hollow, 

 and tilled with coagulated blood. 



The right, functional genital duct, and the left, non-functional genital duct, are l)oth contained 

 in the pallio-visceral ligament, their inner borders following ilosely the right and left anterior 

 viscero-pericardial openings, respectively. 



The pallio-viscei'al and genital ligaments are. like the intestinal and gastric ligaments, composed 

 of double lamella?, containing the organs within them. The ova and their follicle cells and the 

 pericardial glands arc the only organs literally lying in the ccelom. 



The ccjelom is lined with an epithelium compo.sed of flattened ])c>lygonal cells. Upon the 

 anterior wall of the ccelom some of the cells, according to Haller, can be distinguished by their 

 taking a more intense stain from the ordinary coelomic epithelial cells. 



The renal sacs should also be considered as portions of the ccelom, or secondary body cavity. 

 Their complete separation from the main portion of the ccelom is c>xplained liy .some as a result 

 of the displacement of the reno-pericardial openings from the inside of the anterior renal sacs to 

 the surface of the body at one side of the external openings of the renal sacs. According to this 

 view. Nautilus originally possessed Imt one pair of renal .sacs — the anterior, t)eside the apertures 

 of which the pericardial pores are found — while the posterior sacs have been derived l)v a division 

 of the anterior sacs, and a .separation of the two pairs of sacs thus formed. In somewhat the 

 .same manner and at the same time the anterior gills and their ves.sels have divided to form the 

 posterior gills and their vessels. 



The explanation is certainly far-fetched, and can not l)e received with too nuich caution. 

 Other explanations are possible, and it is quite probable that some other will be found in future 

 years which will show that this one is entirely erroneous in its conceptions. 



It is at least as easy to suppose that the posterior gills and renal sacs have been developed 

 independently of the correspt)nding anterior organs and that similarity of function has brought 

 about similaritj' of structure, just as it has in several instances in-adult and embryonic organs of 

 widely separated groups. 



