47 



seem to be dainty in its choice, but to utilise all the organic particles that come within its 

 reach, and into its pover. Even such animals as are provided with a firm calcareous crust, 

 for instance shells and foraminifera are swallowed with equal avidity, and the organic par- 

 ticles of the same rapidly extracted. How, in all probability, the animal obtains its prey 

 we have already considered. That the pedicellaries play an important part in such capture 

 I think is indubitable. I consider it very probable that the animal does not only attack 

 smaller organisms, but also animals or masses of organic matter which are too large to pass 

 through the b.ucal aperture, even when it is extended to its greatest circumference. In this 

 case the folds of the stomach are protruded more or less beyond the bucal aperture, and 

 laid round the object or a part of it; so that the digestive cavity may in this case be said, 

 in a manner, to lie outside of the body. It is by no means rare, especially in the other 

 species Br. endecacnemos, to find specimens in which the folds of the stomach are in this 

 manner protruded through the mouth, in a very remarkable degree, so as even to project 

 far beyond the spines attached to the lower side of the disc, and thereby entirely to conceal 

 the proper border of the mouth (see the delineation in Fauna littoralis Tab. IX, fig. 2). 



b. The digestion. 



From the walls of the stomach there is secreted, during the reception of the ali- 

 ments, a fluid which seems to have a quickly dissolving and decomposing influence on the 

 food; so that in a comparatively very short time the nourishing matter is extracted even 

 from such organisms as, like shell-cased molluscs and foraminifera, are enveloped in a hard 

 calcareous shell. The indigestible residuum of the aliments is, together with the extraneous 

 parts, (the particles of mud) which enter the stomach at the same time, simply thrown out 

 by the same way they came in. But the fluids, which can be more easily assimilated, are 

 received into the upper stomachal cavity, whence they pass into the radial caeca, which will 

 always be found filled with a greater or less quantity of oily juice (chylus). From the main 

 trunks of the radial caeca this juice enters again into thin-skinned lateral recesses, in which 

 probably the absorption or the transfer of the nourishing parts of this juice to the rest of 

 the body, or conversion into blood, takes place. According to my conception, this is effec- 

 ted simply by a transudation through the walls of these lateral recesses, whereby the juice 

 is thus immediately mixed with the fluid contained in the perivisceral cavity. 



c. The circulation of the blood. 



As is well known, Tidemann supposed that he had found in the great Mediterranean 

 star-fish Astropecten aurantiacus a completely developed blood-vessel system of veins and 

 arteries, and assumes therefore in this case a completely developed circulation of the blood. 

 The central organ of the circulation of the blood, or the heart, is considered by him to be 



