On the Structure aud Developmeut of Argiope. 497 



through tlie calcareons part, but their outev end is covered b}' the ciiticle. 

 Tliey are of imiform diametev in the first pavt of their course through the 

 first layer, but when they reach the second layer of King , they expand 

 and end in funnel shaped mouths 'fìgs. 1 and 15 w?;j). The distribution 

 of these canals is very uniform, they mostly lie on liues coucentric with 

 the free edge of the shell. Their course is usually perpendicular to the 

 surface of the shell, though occassionally they bave an oblique direction. 

 They are as a rule single but in the posterior part of the perforate shell, 

 where it is unusually thick, I bave seen branched canals. Similar bran- 

 ched canals are described for Terebratula caput serpentis , and the ca- 

 nals of Crania brauch at their outer extremities. 



The minute structure of the internai skeleton is like that of the inner 

 layer of the shell, there are no canals present, but in Argiope (Cistella) 

 lutea, a species 'considerably larger than those of the Mediterranean', 

 W. H. Dall^ States that canals are present in the substance of the 

 internai skeleton. 



The mantle which lines the internai surface of each shell is formed 

 by two evaginations ofthe body wall. Although the body of Argiope 

 occupies a much greater part of the mantle cavity than is usuai with 

 Brachiopoda, stili it lies almost wholly within the dorsal shell , conse- 

 quently nearly the whole of the ventral and a considerable portion of 

 the dorsal shell, that is the part not occupied by the body, are lined by 

 the mantle. Since the mantle is formed by a duplicature of the body 

 wall it is necessarily double and in some places there are prolongations 

 of the body cavity in which the generative organs lie , in other places 

 the two layers bave fused. 



At the edge of the shell the mantle becomes thickened and forms a 

 number of ridges which are covered by a high epithelium ; the nuclei of 

 these cells stain very clearly. From some sections which I bave pre- 

 pared, I believe, that the ridges of the opposite shells interlock and thus 

 dose the mantle cavity in a very complete mauner. Elsewhere the 

 inner surface of the mantle is covered by a fiat epithelium not very 

 well defined, beneath this lies a number of granular branched connective 

 tissue cells. On the outer surface the mantle is in direct connection with 

 the organic basis of the shell. No setae occur on the mantle of Argiope. 

 Into each of the canals which pierce the shell , the mantle sends a 

 diverticulum. This is a hollow tube which fits exactly into the calcareous 



1 Report on the Brachiopoda obtained by the United States Coast Survoy 

 Expedition, in Charge of S. F. de Pourtalès, with a Revision of the Craniidae 

 and Discinidae, by W. H. Dall. 1871. 



