On the Structure and Development of Argiope. 503 



witb the body wall betweeu the occliisor muscles aucl the ovaiy, the other 

 to the outside of the ovaiy which thus lies betweeu the two layers. It does 

 not extend farther anteriorly than the stomach, being stopped by the liver, 

 or veiy far posteriorly, where it forms a curve to allow the teudons of 

 the occlusor muscles to pass to the ventral shell. The ileo-par ietal 

 band of Huxley is but very slightly represented in Argiope and can 

 hardly be considered to afford any support to the intestine. It lies in 

 the same piane as the gastro-parietal and is seen in fig. 8 where the 

 inner lip of the opening of the segmentai organ is seen to be connected 

 with the wall of the intestine. Besides the mesenteries which are uamed 

 there are numerous irregulär connective tissue Strands which serve to 

 connect the alimentary canal with the walls of the body. In their minute 

 structure the mesenteries consist of a median layer of homogeneous 

 substance coated upon each side by flat cells whose nuclei stain deeply. 



The liver consists of two branched glands lyiug one on each side 

 of the alimentary canal, in that part of the body cavity which is enclosed 

 on one side by the lophophore , on the other side by the dorsal shell 

 anteriorly, and by the gastro-parietal band posteriorly (fig. 3 to 6 li) . It 

 is visible in the fresh state through the lophophore, the branches are 

 thick, rounded at their ends, and not more than six or seven in number; 

 they lie nearly ali in one piane. The greater part of the liver lies in 

 front of the mouth. The stem of the liver is thick with a broad lumen ; it 

 opens on each side into the stomach by a wide mouth. The lumen is 

 continued until the end of each branch. The secreting surface of the 

 tubules is increased by their inner walls being raised into a number of 

 wedge-shaped ridges, so that in transverse sections the lumen has the 

 form of a star. The cells lining the tubules are often very much va- 

 cuolated, and their nuclei lie in their outer ends; in the fresh state they 

 have a brown color. The secretion they form is thrown out into the 

 lumen which in many cases is quite full of it. 



Like other recent observors, I have been uuable to find any thing 

 corresponding to a centrai circulatory organ, or to the system of arteries 

 and »accessory pulsatile organs« described by Hancock. The blood is 

 contained in a number of vessels which ruu irregularly in the tissues of 

 the body, but which chiefly lie in the mantle and that part of the body 

 wall lining the shell. It is not possible to make out very distinct walls 

 to these vessels, which appear to be mere slits in the tissue; they com- 

 municate, as was mentioned above, with the papillae of the shell , and 

 are especially numerous at the posterior end of the ventral shell, and in 

 the angle formed by the posterior border of the triangulär septum and 



33* 



