HISTORY OF BALANOGLOSSUS AND TORN ARIA. 425 



stages; in the youngest specimens observed, the muscular band connecting the 

 extremity of the water-system to the base of the eye-spots is present These two 

 features are not known in any other Echinoderm larva, and were sufficient to have 

 shown the possibility of Tornaria proving the larva of an Annelid. In the well- 

 known Annelid larva of Loven 1 (which, according to my observations, 2 develops into 

 a Nemertian, while Schneider 3 thinks it is the larva of Polygordius) we find the same 

 muscular band starting from the base of the eye-specks, and in older stages the 



belt of vibratile cilia. Owing, however, to the great number of 



6 



below the anterior part of the larva, and the presence of a prominent anterior ring 

 of vibratile cilia above the mouth, the close resemblance between Loven's Larva and 

 Tornaria is not so striking at first sight as it really is. In Tornaria the prominent 

 belt of large vibratile cilia appears at a comparatively late period, yet long before 

 any of the rings of the posterior part of Balanoglossus ; while in all Annelid larvae 

 which have a similar anal belt of vibratile cilia this belt is the earliest to make its 

 appearance, long before there is any trace of the formation of the rings of the 

 posterior part of the body. I would refer to the figures of Annelid lame given by 

 Milne-Edwards, 4 Sars, 6 Busch, 6 Miiller, 7 Claparede, 8 Max Miiller, 9 Krohn, 10 Metschni- 

 koff, 11 and myself, 12 for comparison with Tornaria. 



The figures of Tornaria given in this paper precede immediately its transformation 

 into young Balanoglossus ; for the earlier stages I would refer to the figures given 

 by Miiller, Metschnikoff, and myself. The oldest stages of our Tornaria difier mate- 

 rially from those described by Metschnikoff. He speaks of a second smaller anal band 

 of vibratile cilia, between the broad band and the anal opening. I have not found this 

 second band in any specimens of our Tornaria, and in our species this band does not 

 exist. Metschnikoff represents the " Wurstformige Korper " as appendages of the intes- 

 tine, and as different from what he has called the lateral plates, or appendages of the 



Loven. Jakttagelse ofser Metamorfos lios en Annelid, K. Vet. Akad. Ilandl. Stockholm, 1840, p. 93. 



Agassiz, Alkx. On the Young Stages of a few Annelids, Ann. Lyceum Nat. Hist., New York, 1866, p. 303. 



Schneider. Bau u. Entwickelung v. Polygordius, Mull. Arch., 1868, p. 51. 



Mxlne-Edwards. Ann. Sc. Nat., III., 1845; Ann. Sc. Nat., VIII., 1847. 



Sars. Archiv f. Naturg., I., 1845. 



Busch. Bemerk. ucber Anat. u. Entwickel. einig. Wirbellos. Thiere, 1851 ; Mull. Arch., 1847. 



Muller. Sitzungb. Akad. Berlin, 1851, 48. 



Claparede. Boob, iiber Anat. u. Entwickel an d. Kiiste v 



Max Muller. Muller's Archiv, 1850, 1855. 



Krohn, A. Muller's Archiv, 1851 ; Krohn u. Schneider. Mull. Arch , 1867 ; Annelid larveu mit poros. Hullen. 



Clapauede u. Metschnikoff. Zeitsch. f. Wiss. Zool , 1868. 

 18 Agassiz, Alex. Young Stages of Annelids, g, a. 



Norma 



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