48 



the peculiar meinbranous organ which accompanies the stone canal, and which in his opinion 

 connects itself with a dorsal and a ventral annular vessel whence the other blood vessels 

 issue; the dorsal annular vessel with its ramifications representing the venous system, and 

 the ventral annular vessel with the branches issuing from it, the arterial system. This 

 complicated arrangement of the blood-vessel system described by him, which would also 

 necessarily presuppose a complete circulation of the blood, has been, as it reasonably might 

 be, considered referable to all star-fishes, without any one, so far as I know, having subse- 

 quently been able by direct investigation to demonstrate anatomically the existence of this 

 system of vessels in other star-fishes, and thereby to confirm Tidemann's statements. Neither 

 have I, as already mentioned, been able to discover this system of vessels in the Brisinga. 

 The only part which in this animal, as well as in other star-fishes, may easily be indicated 

 is the so-called heart, the real nature and destination of which still appear to me to be highly 

 problematical. Also in the Brisinga this organ (Tab. VI, fig. G h, fig. 8) accompanies the 

 stone-canal, extending from the ventral to the dorsal side of the disc, where it terminates 

 at a short distance from the stone-canal on the inner side of the madreporic body. The 

 complicated system of veins, which according to Tidemann's description is supposed to stand 

 in connexion whith the heart I consider to be something quite diff'erent, namely simply 

 ligaments serving to attach the stomach and the radial ca;ca to the dorsal skin. By repeated 

 careful dissections I have succeeded in obtaining preparations of all these ligaments in 

 ■ their natural connexion with each other and with the adjacent parts (see Tab. \T, fig. 6) 

 whereby a somewhat complicated structure is exhibited, in the chief features of which it 

 is easy to recognise the arrangement indicated by Tidemann for the supposed veins. I have 

 however been able at the same time, to ascertain by satisfactory evidence the real nature 

 of all these parts, differing widely from that of blood-vessels. As regards the supposed 

 ventral, or so-called arterial blood-vessel system, my investigations in the Brisinga and other 

 star-fishes have led me to the conclusion that we have only here to do with a system of 

 narrow canal-like sinus, without any particular walls, covered immediately below by the chief 

 parts of the nervous system, and not in any proper sense entitled to be called blood-vessels. 

 The blood is thus in the Brisinga, and as I have reason to believe also in other star- 

 fishes, not inclosed in a special system of vessels, but freely suspended in the whole peri- 

 visceral cavity (cajloma) where it immediately surrounds and laves all the interior organs. 

 That there should also be found in the perivisceral cavity a considerable quantity of water 

 taken in from without, I do not regard as forming any objection to this opinion; on the 

 contrary I hold such a mixture of blood to be quite necessary for its maintenance and puri- 

 fication ; as special breathing apparatus is, at least in the Brisinga, entirely wanting. The 

 locomotion of the blood-fiuid contained in the perivisceral cavity is brought about by a 

 lively ciliary movement of the whole interior surface of the skin, partly no doubt also by the 

 contractions and expansions of the skin itself and of the central part of the digestive cavity 

 or stomach. There can thus be no question here, properly speaking, of any real circu- 



