. Catalogue of the British echinoderms in the British Museum (Natural History) by F. Jeffrey Bell. Echinodermata; Marine animals -- Great Britain. 10 ECHIXODERMA. the madreporite becomes very extensive, and occupies the centre of what remains of the calycinal area. In Ophiuroids the stoue-canal ends on one or several of the mouth-shields. lu Crinoids the water- vascular system opens by one or a number of separate pores. In the Holothurians the stone-canal is connected with the wall of the body in the Elasipoda and a few others, to the mesentery in others, and in many hangs freely into the body
. Catalogue of the British echinoderms in the British Museum (Natural History) by F. Jeffrey Bell. Echinodermata; Marine animals -- Great Britain. 10 ECHIXODERMA. the madreporite becomes very extensive, and occupies the centre of what remains of the calycinal area. In Ophiuroids the stoue-canal ends on one or several of the mouth-shields. lu Crinoids the water- vascular system opens by one or a number of separate pores. In the Holothurians the stone-canal is connected with the wall of the body in the Elasipoda and a few others, to the mesentery in others, and in many hangs freely into the body-cavity ; in a number of cases there is more than one canal. Development.—Although it is possible to understand the diagnosis of an Echinoderm without knowing anything of its life-history, it is not possible to have an intelligent interest in them without desiring to know something of how it comes to be what it is. Developed, like all other Metazoa, from an egg, there very rarely appears to be that mode of development without the inter- ference of the male element, which is seen in various Arthropoda. The sexes are generally but not always separate. There is often some kind of sexual congress though no copulation. The fertilized ovum undergoes division, and gives rise to a larva which is ciliated all over; these cilia then become arranged in one curving band (as in Aiu-icularia, the typical larva of Holothurioids), or in two, as in Bipinnaria (the typical larva of Asteroids), or in several circlets as in the larva of Antedon. All these larvae are bilaterally symmetrical. They generally become very remarkable in shape owing to the development of lobes which may unite to form an organ larger than. Flnfcvs. Bipinnaria. the young itself, or several lobes may form processes, or within the lobes rods may be developed and give rise to bodies compared, not inaptly, to a painter's easel {Pluteus). These larvte may, as in the case of Bipinnaria asterigera, be more than an inch in size,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectechinod, bookyear1892
