DEVELOPMENT 19 



Tornaria was described and named by Johannes Mliller, who 

 regarded it as the larva of a Starfish, 1 in spite of his intimate 

 knowledge of the development of these animals. Its correct syste- 

 matic 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 

 ?th inch). 



O * 



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. Jcrohni, which occurs on our south coast, 2 the 

 ciliated band has a wavy course. In the West Indian larva 3 

 shown in Pig. 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. 4 At the apex of the 

 larva is a thickening (<?) 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 (in}, 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 () at the posterior pole. 



On the dorsal side is a pore, the " dorsal pore " (d.p.\ which 

 leads into a thin-walled sac (&.c a ) destined to become the pro- 

 boscis-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 



1 Cf. Spengel, Monogr. p. 363 f. 



2 Bourne, J. Mar. Biol. Ass. (N.S.), i. 1889-90, p. 63. 



3 This closely resembles T. grenacheri, but see Willey, op. tit. p. 285. 



4 Haldeman, Johns Hopkins Univ. Circ. vi. No. 54, 1886, p. 45. 



