. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 273 ECniXODERMATA. have been found in the Echinoidea and Asteridea. In the former {Cidaridea) there ax-e, on special plates {ocular j)lates), at the apical pole, five tentacle-like prominences, in each of which a nerve ends. The eyes of the Asteridea are most accurately known. According to Ehrenberg's discovery, they have the form of red pigment spots, and lie on the ventral side of the rays at the distal end of the ambulacral groove. They are spherical pedunculated prominences, and the convex surfa
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 273 ECniXODERMATA. have been found in the Echinoidea and Asteridea. In the former {Cidaridea) there ax-e, on special plates {ocular j)lates), at the apical pole, five tentacle-like prominences, in each of which a nerve ends. The eyes of the Asteridea are most accurately known. According to Ehrenberg's discovery, they have the form of red pigment spots, and lie on the ventral side of the rays at the distal end of the ambulacral groove. They are spherical pedunculated prominences, and the convex surface is covered by a simple membrane, which hides a number of conical simple eyes (fig. 221). The simple eyes appear to have their axes directed towards a common point. They each con- sist of a red mass of pigment surrounding a refractive body, and a nervous apparatus. Reproduction is mainly sexual, and separate sexes are the rule. Only Sy- napta and Aviphiura are hermaphrodite. The organs of reproduction of the two sexes are ex- tremely alike, so that if it were not that the colour of the generative products is different,—the seminal fluid is mostly white and the ova red or yellow,— a microscopical examina- tion of the contents of the generative glands would be the only means of distinguishing between them. Sexual differences of the external form or of definite parts of the body are only vei-y rarely present, since as there is no copulation the sexual functions are usually confined to the secretion and prepai-ation of the generative material. Ova and spermatozoa, with some rare excep- tions, first come in contact in the sea water outside the body of th3 mother. Internal fei-tilization, which is very rare, occurs in several viviparous species of Amjjhmra and Pliyllopliorus. The niimber and position of the generative organs are generally in strict correspondence with the radial structure; nevertheless there are numerous excep- tions to this. In the regular Echinoidea, five-lob
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
