XV. 



The History of Balanoglossus and Tornaria 



BY ALEXANDER AGASSIZ. 



Communicated December 10, 1872. 



Among the many pelagic invertebrate larvae discovered by Muller, of which the 

 development remained long unknown, Tornaria is one of the most interesting. 

 Previous to the preliminary notice given by Metschnikoff 1 in 1869, it had been 

 taken for granted that Tornaria was the larva of some genus of star-fish. Discovered 

 by Muller 2 in 1848, Tornaria was subsequently studied by Krohn 8 in 1853, Muller 

 gave a very full account of the younger stages; Krohn's paper, though not adding 

 materially to our knowledge of this larva, complemented the descriptions of Muller 

 in a few particulars. Nothing further was written on the subject till 1866, when 1 

 published a short paper on some points of the development of Tornaria 4 which had 

 not been noticed in the young stages described by Muller. This additional infor- 

 mation seemed to settle definitely the star-fish nature of the larva, and I accepted 

 unhesitatingly, as well as my predecessors, Muller's views of the affinities of Tornaria 

 It was only subsequent to the publication of my paper that Dr. Fritz Muller 



w 



called my attention to a so-called heart, discovered by him in a species of Tornaria 

 from the shores of Desterro. This heart, situated at the base of the canal leading 



from the water-system to the dorsal pore, is the only organ of Tornaria throwing 



1 



6 



some doubt on the then generally accepted systematic position of the larva, and 

 began seriously to doubt the correctness of the homologies I had carried out between 

 the arms of Brachiolaria edged with vibratile cilia and dotted with pigmentrcells and 

 the similar ciliated bands of Tornaria. 



Muller, Krohn, and myself attached altog 



the large promi 



1 Metschnikoff, El. Gottinger Nachricbten, 1869, No. 15, p. 287. 



' Muller, J. Ueber die Larven u. die Metam. d. Echinod. Abhand).. H, Berlin, 1849 ; Ueber die Larven u. die 



Metam. d. Holoth. u. Aster. Abhandl. III., Berlin, 1850. 



* Krohn, A. Muller's Archiv fur Anat. u. Phys., 1853. 



* Agassiz, Alex. Tornaria, Ann. Lyceum Nat. Hist., VIII., New York, 1866. 

 s Muller, F. In Keferatein's Bericht for 1867. 



VOL. IX. 58 



