Notes on the Embryology of Starfishes. 241 



larvae (Tornaria) and the larvae known to give rise to true Star- 

 fishes (Brachiolaria), that it will be a matter of the utmost inte- 

 rest in the study of Echinoderms to determine the genus of 

 Starfishes to which Tornaria belongs. The presence of an anal 

 ring of vibratile cilia analogous to that of Pneumodermon, with 

 which I have had frequently the opportunity of comparing it, 

 and the peculiar nature of the water system, are features utterly 

 unlike those of any other Echinoderm Pluteus. 



The changes of outline of Tornaria, with advancing develop- 

 ment, are by no means to be compared with the extraordinary 

 transformations characteristic of the development of a Pluteus 

 or a Brachiolaria. The youngest plutean forms observed by 

 Muller* can readily be recognised as forming part of the same 

 cycle of development with the adult Tornaria. While the young 

 Sea-Urchin or Ophiurean or Asteracanthion Pluteus cannot be 

 recognised as such until the connecting links are traced. 



The general form of our Tornaria is cylindrical with a slightly 

 conical base and summit (Figs. 3, 8). They always retain their 

 cylindrical outline, and do not become flattened with increasing 

 age as Brachiolaria and other plutean stages of Echinoderms. 

 On comparing the young Tornaria, Fig. 1, with a young Bra- 

 chiolaria, Fig. 11, we readily recognise the anal (v) and oral (v') 

 plastrons, with the broad horseshoe-shaped groove between 

 them (a) in which the mouth (m) opens. The oral plastron 

 laps over the opening of the mouth, concealing it entirely ; this 

 is best seen in profile (Figs. 3, 8 m). The vibratile chords 

 which bind the plastrons resemble the chords of the Brachio- 

 laria in their earlier stages, and the only tendency we have 

 towards the formation of arms are the slight projections (e e' e", 

 Figs. 3, 6, 8) on the sides of the anal and oral chords. The chords 

 do not extend simply on the edge of the plastrons ; towards the 

 oral extremity we find both the oral and anal vibratile chords 

 forming on the surface of the body well marked loops (Figs. 1. 



# * See Muller. Memoir II. Plate 5. 



