{19}Tornaria was described and named by Johannes Müller, who regarded it as the larva of a Starfish,[28] in spite of his intimate knowledge of the development of these animals. Its correct systematic position was first demonstrated by Metschnikoff in 1869. The larva agrees with many other pelagic forms in being excessively transparent. The form described by Spengel as _T. grenacheri_ attains the remarkable length of 9 mm. (nearly ⅖th inch). The full-grown larva is usually ovoid, and a complicated "longitudinal" band of cilia runs in several loops over its anterior two-thirds. In side view, part of the surface limited by the ciliated band appears like a T with a double outline, the cross piece being bent downwards on each side, so as to form an anchor-like curve, the middle of which is at the anterior pole of the larva. In _T. krohni_, which occurs on our south coast,[29] the ciliated band has a wavy course. In the West Indian larva[30] shown in Fig. 8 A, the ciliated band is produced into numerous tentacles, which fringe the sides of the T-shaped areas or grooves of the surface. These grooves and the cilia which border them are used for conveying food to the mouth.[31] At the apex of the larva is a thickening (_e_) of the ectoderm, bearing two eye-spots. The main locomotor organ is a simple transverse band (_c.r_) of "membranellae," vibratile structures composed of fused cilia. The mouth (_m_), on the ventral side, leads into the oesophagus, and this into the stomach (_s_). The latter is separated by a marked constriction from the intestine, which opens by the anus (_a_) at the posterior pole. On the dorsal side is a pore, the "dorsal pore" (_d.p._), which leads into a thin-walled sac (_b.c_^1) destined to become the proboscis-cavity of the adult. To the right of the dorsal pore lies the pulsating "heart," which apparently becomes the pericardium of the adult. Bourne and Spengel regard it as a right proboscis-cavity. In the older larvae, the second and third body-cavities appear as paired thin-walled sacs in close contact with the hinder part of the stomach. The skin is very thin, and the five body-cavities do not nearly fill the space between it and the {20}alimentary canal. This space becomes obliterated for the most part by the enlargement of the body-cavities, and its last remains persist, as in many other animals,[32] as the vascular spaces of the adult.