THE HISTORY OF BALANOGLOSSUS AND TORNARIA. 



4 



23 



ment of Echinoderms. 



The 



majority of English naturalists 



views without further investigation. 



have adopted Huxley's 



Torn 



presents the startling anomaly of 



larva, at least till lately so considered by 



an Annelid 

 Huxley; b 



d 



seems at first 



ght 



a 



an apparently genuine Echinoderm 



iters on the subject, developing into 



conclusive proof of the views entertained by 



I think I shall show in the description of the development of Tornai 



the position taken by Huxley is not strengthened, and the gap left between tlw 

 mode of development of Planarians and other Annelids, as compared with the develop 



of Echinoderms, is as g 



as 



pite of the very striking analogy in the 



mode of development of some Echinoderms (especially Holothurians and Coma ml 

 with that of Nemertians, 



Tornaria tends, on the c( 



as 



ntrary 



shown by Muller 1 and Metschnikoff. 2 The history of 



relationship between the 



show a much closer 



Nemertians and the Annelids proper than is generally credited, the development and 

 anatomy of Balanoglossus showing it to be closely allied to Terebellidae, Clymenidae, 



now 



and allied Annelids, as already suggested by Metschnikoff and Kowalevsky. And, 

 that we know its ultimate development, the larva presents points of resemblance to 



well-known Annelid 



(Loven's Larva) which are apparent 



onstrated, but so completely hidden by the more p 

 features as readily to have escaped notice. 



enough when dcin- 

 pseudo-echinodennal 



The presence of the 



ystem, rid 



o 



with its spurs upon the anterior 



extremity of the alimentary canal, and connecting with the exterior by means of 

 canal and a dorsal pore, exactly as in the larvae of the Echinidae, Star-fishes, Ophurian 

 and other Echinoderms, seems at first sight an overwhelming proof of the positio 

 taken by Huxley. But, as I have already shown in my Embryology of the Star-fish 

 Huxley, misled by the names given by Muller to some of these larvae (" Wurmfdrmig 

 Larven"), has revived the old opinion of Oken, and associated the Echinoderm 

 with the Articulates. The hypothetical form to which Huxley reduces these larva 



3 



to 



ake his 



com pa 



and to d 



his inferences 



w h 



ha 



been 



observed, and as far as we now know does 



The larvae of all the principal 



typ 



have been described by Muller, Krohn, Thomson, Metschnikoff, and myself. 



The development of the water-system from the digestive cavity has not been traced 

 in Tornaria ; while the lappets of Tornaria, which have nothing to do with the water- 



Wurml 



Muller, J. Ueber eine eigenthumhche 

 4 Metschnikoff, El. Studien ub. d. Entwickel. der Echinod. u. Nemertinen, fcfera. Acad. St. Petersb., 1869, 

 XIV. No. 8. 



* Agassiz, Alex. Embryology of the Star-fish, 1864, p. 60. 



