ANATOMY, HISTOLOGY, MORPHOLOGY, AND FHYLOGENY. Ech. 23 
The ancestor of Synapiids was without radial water-vascular canals, 
which have never been developed in the group. The author does not 
believe radial symmetry to have been acquired by fixation. 
Cuenot (4) describes the blood and lymphatic organs of Echinoids , 
pp. 613-626, Asteroids , pp. 626-628, Ophiuroids , pp. 628-630, Crinoids , 
pp. 630-635, and Holothurians , pp. 635-641. A resumi and comparison 
of the results obtained in Echinoderms and other animals is given, pp. 
641-656. Cf. CuriNOT (1). 
For a description of the nervous system of Asterias rubens , see 
Demoor & Chapeaux, pp. 112-117, The superficial epithelium is 
composed of sensory cells and supporting cells. The infraepitbelial 
fibrillar plexus consists of nerve fibrils and ganglion cells, for the most 
part fusiform. There is a fibrillar zone under the peritoneal epithelium, 
which is believed to be connected with the epithelial nervous system by 
nerve fibrils. 
Durham has studied, in Asterias rubens and some other Echinoderms, 
the histology of the dorsal organ (ovoid gland) and the so-called blood- 
vessels coming from it, for which he proposes the term “ haemal strands,” 
distinguishing them as circumoral, radial, genital, and gastric. The 
whole “ haemal system ” is contained in the perihaemal canals, and the 
dorsal organ in the axial perihaemal space. 
The dorsal organ of Asterias contains — (1) fibres, possibly contractile, 
running longitudinally ; the organ contracts when irritated by a needle : 
(2) large numbers of leucocytes, some containing granules, and some 
with pseudopodial processes projecting from the surface of the organ. 
The whole organ consists of a number of anastomosing haemal strands. 
In Cribrella (2mm. in diameter) there is a single water pore com- 
municating with the axial sinus, into which also the free end of the 
water tube opens. The cavity of the axial sinus extends amongst the 
strands which form the dorsal organ, as “ intercanalicular ” spaces. In 
the dorsal organ of Echinoids there exist epithelium-lined spaces com- 
municating together, and with a cavity extending longitudinally along 
the organ ; this system of spaces has free communication with 
both the water pores and the water tube, though in certain forms 
only, not in Echinids. This space bears the same relations as, and is 
homologous with, the axial perihaemal sinus in Asteroids. The presence 
or absence of free communication with the water and madreporic 
tubes depends upon whether the embryonic condition has been re- 
tained or lost. If the axial sinus (left anterior enteroccele of Bury) 
be imagined to contract upon the enclosed organ and fuse with its 
surface, except along the stone canal, the condition is obtained which 
exists (Prouho) in Dorocidaris. The author does not favour Sarasin’s 
nephridial theory of the dorsal organ, and looks upon S.’s nephro- 
stomes in Asthenosoma, which he was unable to find in Spatangus 
purpureus and Echinus sphcera , as communications of the axial sinus 
with the coelome* 
For oogenesis and spermatogenesis of Asterias vulgaris , see Field. 
