ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 959 



spines are longer than in those which live on sand ; this difference 

 points to the locomotor function of these appendages. 



The form of the large sac which constitutes the chief part of the diges- 

 tive tract varies in different species ; in Ophioglypha albida it has fiye 

 large interradial and five small radial lobes, while in Opliiotlirix rosula it 

 has only the interradial lobes. In form the digestive tube of Ophiurids is 

 absolutely comparable to that of a young Luidia before the development 

 of the radial C8eca. There is no muscular layer, or it is reduced to a few 

 scattered and unimportant fibres ; the tube is firmly attached to t^ie test 

 by a number of mesenteric bands. The glandular cells which give the 

 tube its dark coloration are similar to the granular cells already 

 described by the author in Asterids, but there is no nervous layer among 

 the digestive cells as there are in them. In the Ophiurids proper the 

 prolongation which connects the nerve-ring with the digestive tube is 

 solely composed of connective fibrils and epithelial nuclei, without any 

 trace of nerve-fibrils, while in the Euryalids it is altogether nervous. 

 Ophiuroids feed on dead or inert material which they gnaw with their 

 peristomial teeth ; the digestive tube takes no part in the prehension of 

 food. 



M. Cuenot differs from preceding describers of the nervous system, 

 who, he finds, have taken epithelial nuclei for nervous cells. As in the 

 Asteroids there is a nervous ring with radial cords, but while, in the 

 former, the central parts are continuous with the digestive tube and the 

 external epithelial investment, and are as much epithelial as nervous, in 

 the latter the peripheral nerves and their branches to the spines cor- 

 respond to the superficial nerve-plexus ; the digestive nervous band is 

 found in Euryalids only; the Ophiurids appear to be peculiar in the 

 nerves which supply the muscles of the arm and the disc. The only 

 sensory organs are those of touch, represented by the spines, the ambu- 

 lacral and the terminal tentacles ; the olfactory sense which informs 

 Ophiurids of their prey can only be exercised by the tentacles, the 

 nerves of which are sufficiently near to the external medium. 



The fluid of the blood is sea- water with an exceedingly small quantity 

 of albumen dissolved in it ; the corpuscles are exactly similar to those 

 of Asterids. The colouring matter is not, as has been stated, htemo- 

 globin, but a ferment which converts peptones into non-dialysable 

 albuminoids. The amoebocytes and their albuminogenous granules are 

 produced by lymphatic glands, and appear to be formed in just the same 

 way as in Star-fishes. 



In Ophioihrix rosula the respiratory sac is not a mere involution, 

 but sends out a prolongation which passes into the interradial muscle, 

 in such a way as to carry oxygenated fluid to it, and to bring away its 

 products of excretion. The uric salts, guanin, xanthin, &c., pass by 

 osmosis through the walls of the respiratory sacs. 



In his account of the ambulacral system the author differs consider- 

 ably from M. Koehler. He regards the sand-canal as " un simple 

 souvenir morphologique " which may have some function in the embryo, 

 but has almost no importance in the adult. 



A somewhat detailed account is given of the vascular system, in which 

 views different from those of preceding observers are expressed. 



With the exception of AmpJtiiira squamata, all Ophiurids have the 

 sexes separate. The genital organs are of two different types : in 

 Ophiocoma, OpMoglypha, and OpMomyxa, there are a series of caeca on 



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