On the Structure and Developmeut of Argiope. 499 



had nothing to do with blood corpiiscles but performed some other 

 function possibly a secretoiy one. This view that the papillae are not 

 respiratory is, I believe, correct. The wall of the outer end, where the 

 blood Comes into closest contact with the external medium, is somewhat 

 tbickened, the papillae are everywhere covered by a thick layer of dense 

 periostraeum ; they occur very uniformly distributed in both shells, being 

 as numerous where one shell is lying imbedded in the object on which 

 the Argiope rests, where no gaseous change couldftake place, as in the 

 other free shell. These facts argue greatly against the view of respira- 

 tion being carried on by the mantle papillae and to some extent support 

 the view which I bave adopted as regards these organs. I believe they 

 exist for the purpose of conveying nutriment to the shell. It is not pos- 

 sible to see the blood flowing in these canals, but I believe it passes 

 in and out, bringing nourishment to the organic network which surrounds 

 every calcareous spicule, very much as the blood is forced in and with- 

 drawn from the tentacles of Phoronis. By counting the number of 

 papillae in a given area of young and old shells Van Bemmelen has 

 shown that the growth of the shells does not take place by Intussus- 

 ception, but the increase must occur at the edge. Thus the function of 

 the old papillae is more closely connected with the nutrition than with 

 the growth of the shell. But that this must be an important function is 

 shown by the size of the shell, often many times the size of the body and 

 by the proportion of the organic to the inorganic constituents. 



One fact which seems at first opposed to this view , is that no pa- 

 pillae are found in the internai skeleton. But these are thin and delicate 

 and, it is quite reasonable to suppose, may be nourished by the numerous 

 blood vessels, running in the mantle which everywhere covers them. 

 And in Argiope (Cistella] lutea , where the skeleton is probably much 

 coarser, Dall states expressly that the internai skeleton is punctate. 



The shell of Argiope can only be opened a very little way, without 

 tearing the tissues of the body wall. When we open the shells wide, 

 the body can be seen lying almost entirely in the dorsal shell and covered 

 for the greater part by the lophophore. The posterior end of the in- 

 testine will probably be seen protruding through the torn body wall 

 towards the ventral shell (fig. 11). The ovaries will be seen lying a 

 pair in each shell, those of the dorsal shell, with some branches of the 

 liver, are seen through the semi-transparent lophophore. 



The lophophore lies entirely in the dorsal shell, it forms a great part 

 of the body wall of the animai. The shape is an oval, the border run- 

 ning parallel with the margin of the shell, except at the anterior median 



