422 ■ MEMOIRS OF THE AMERICAN ACADEMY 



po 



it band of vibratile cilia separating the body of Tornaria into two such unequal 

 tions. The presence of a somewhat similar circular band in the larvae of Holo- 

 thurians and of Comatulae seemed a powerful argument, in addition to other 

 important structural evidence, in favor of the echinodermoid character of the larva. 

 The analogy between Tornaria and the earlier stages of Brachiolaria is so great that 

 in my paper on the Embryology of the Star-fish I called one of the early stages of 

 Bipinnaria the "Tornaria stage." This striking resemblance is, however, only an 

 analogy, as a memoir published by Metschnikoff in 1870 1 leaves no doubt that Tor- 

 mina is the larva of an Annelid and has nothing to do with the Star-fishes. 



The exceptionable character of the development of Tornaria made it desirable that 

 the observations of Metschnikoff should be repeated, and the genus of Annelids, of 

 which it is the larva, definitively determined. MetschnikofF threw out the hint that it 

 was, if not Balanoglossus, at least a genus most closely allied to it, — a view which is 

 fully confirmed by the observations I have made of Tornaria, and of a species of Bala- 

 noglossus from the coast of New England, connecting the young Annelid raised direct- 

 \y from Tornaria with very small specimens of Balanoglossus found buried in the sand. 

 MetsehnikofT certainly showed great sagacity in recognizing as the larva of Balano- 

 glossus the young Annelid he first found pelagic in Naples; 2 but the discrepancy 

 between the two stages then known is so great that his view could hardly be accepted 

 without more tangible proof The young Annelids which I succeeded in raising 

 directly from Tornaria are considerably older than any observed by Metschnikoff, 

 and they are at the same time but slightly younger than very young specimens of 

 the Balanoglossus found living upon our beaches. 



Huxley/ in his report upon the researches of Miiller, proposed to unite the Echino- 

 derms with the Articulates ; but, as he based his opinion entirely upon the figures of 

 Miiller, and not upon original investigations, his conclusion, however ingenious and 



original it may be, and based upon very striking analogical resemblances, is nothing 

 but a hint thrown out for the benefit of investigators. Miiller 4 himself regarded the 

 analysis of his paper as most ingenious, but by no means as conclusive ; although at 

 that time he had already discovered the peculiar mode of development of some Plana.- 

 rians apparently most closely allied in its general features with the plan of develop- 



1 Metschnikoff, El. Untersuchungen ueber die Metamorphose einiger Seethiere, Zeitschr. f. Wiss. ZooL, 1870, 

 p. 131. 



f Metschnikoff, El. Die Larve v. Balanoglossus, Mull. Arch. 1866, p. 592. 

 • Huxley, T. H. Report upon the Researches of Miiller, Ann. Mag. N. H., VIIL, 1851. 



4 Mulleu, J. Ueber den Allgemeinen Plan in der Entwickelung d. Echinodermen, 1853, p. 19. See also Agassiz, 

 Alex. Embryology of the Starfish, 1864. 



