^J8P M. R. Leuckart on the Young States of some Annelides. 



ithis also that Quatrefagcs has derived the name of his species. 

 r,The length of the developed animal is from 2^ to 3 inches, — that 

 joi the two tentacular cirri, 9 lines. The only thing that might 

 perhaps be urged with reason against the identity of the two 

 animals, is the circumstance that the first segment of the body, 

 according to Quatrefages, is destitute of the dorsal pedal tubercle ; 

 but with regard to this point of difference I should be rather in- 

 clined to suppose that there is an error of some kind. Eyes are 

 wanting in the developed animal, as in many other mature 

 worms (and Mollusca) which possess those organs in their young 

 state. The distinction which appears in this respect between the 

 larvae and the mature animals, only shows that Quatrefages has 

 established his new^ genus Malacoceros without sufficient reason, 

 for the want of eyes is the only character by which it is distift- 

 guished from Nerine. 



^ The difference of habitat appears to be of no consequence, 

 .^especially as our larva has a tolerably wide distribution. I cer- 

 tainly do not know where Busch observed his specimens ; but 

 J. Miiller states (Arch, fiir Anat. 1854, p. 92) that he has found 

 it at Marseilles. Miiller how ever only speaks of a very " similar ^' 

 larva, but, apparently, merely because his specimen wanted the 

 'long spines of the first segment. It is with reason that J. Miiller 

 also points out the great similarity that exists between the 

 large spine-like bristles of our Nerine larvse and the strong 

 bristles of the singular Mitrarice. I think that this circum- 

 stance may even justify us in supposing that the tufts of bristles 

 in Mitraria are also mere larval organs. At any rate it seems 

 to me that Mitraria is scarcely anything but the larva of an 

 Annelidc with a provisional apparatus of bristles, as indeed 

 ..Miiller himself has lately indicated {loc. cit. sup.). It is much 

 .to be regretted that Quatrefages could not follow the develop- 

 ment of his HermeUa-l'dYYie for a longer period ; we should then 

 probably have obtained further data for the elucidation of the 

 species of Mitraria. I w ill not however assert directly that the 

 Mitraria are actually larvse of Hermellcej for that would be going 

 ttoo far with our present knowledge, although the elongated capi- 

 tate bristles, which J. Miiller has described, together with the 

 ordinary spines, in the species observed by him, remind one un- 

 mistakeably of the forms of the peculiar palea3 of the Hermella. 

 As regards Mesotrocha and its metamorphosis into Chato- 

 pteruSj M. Miiller has given his interesting observations upon 

 this subject in full in the Archiv fiir Anat. und Physiol. 1855, 

 p. I. In connexion therewith M. Miiller also mentions the 

 larva discovered by Busch, the relations of which to Cliadopterus 

 pcrgamentaceus I have endeavoured to prove, and expresses his 

 opinion that it does not belong to the genus Chatopterus itself, 



