The artificial production of echinoderm larvæ with two water-vascular systems, and also of larvæ devoid of a water-vascular system

Abstract
The development of Echinoderms has been characterised, and with justice, as the most remarkable ontogenetic change in the animal kingdom. For the larva is an almost perfect example of a simple, bilaterally symmetrical Metazoon, and the amazing thing is, not that the radially symmetrical adult should develop out of a bilaterally symmetrical larva, but that the axis of symmetry of the radial adult should cut the principal axis of the bilateral larva at an angle which approaches 90°. In the three orders Asteroidea, Ophiuroidea, and Echinoidea, the general anatomy of the early larva is of the same type. In all three groups the larva possesses a simple alimentary canal, consisting of a conical œsophagus opening by a wide mouth, a globular stomach, and a sac-like intestine opening by a narrow anus and directed forwards, so that the whole alimentary canal has the form of a U. On each side of the œsophagus a flattened cœlomic sac is situated; of these, the left sends up a vertical outgrowth termed the pore-canal, which fuses with the dorsal ectoderm, and opens to the exterior by a pore called the madreporic pore. Each cœlomic sac subsequently grows backwards, so that its posterior portion lies beside the stomach, and this portion later becomes separated by a constriction from the rest. Consequently, each sac becomes divided into an anterior and a posterior cœlom.

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