264 M. R. Leuckart on the Young States of some Annelides. 



similarity existing between it and the supposed larva oiLeucodore 

 ciliata, figured by Oersted (Consp. Annul. Danic. tab. 6. fig. 96). 

 It is true that I have not this figure by me at present, but as 

 far as I can remember, exactly the same powerful bristles occur 

 in this, which so remarkably characterize our larva in the first 

 period of its life, and these are also exactly similar in arrange- 

 ment and development. I am not certain whether Oersted has 

 recognized the peculiar structure of these bristles, but I scarcely 

 think he can have done so, as otherwise I should hardly have 

 approximated to it a larva with simple (permanent) bristles 

 which I found in Heligoland, as was the case in the papers 

 which I published in conjunction with Frey (p. 99). 



Similar temporary bristles occur however in other Annelidan 

 larvse, and even in some which are considerably removed from 

 our animals. I will not refer to the larva figured by Busch 

 (tab. 7. figs. 5 & 6) as an example of this, as its derivation is still 

 entirely unknown, and it might possibly be nearly allied to our 

 Spio. But I may recall the fact that Quatrefages has described 

 an exactly similar structure in the larva of the genus Hermella 

 (Ann. des Sci. Nat. 1848, vol. x. p. 153). It is true that there 

 are no observations as to the subsequent shedding of these 

 bristles, but nevertheless there can be no doubt upon the point, 

 for the developed Hermella are destitute of them, as I know 

 from my own observations. These bristles have nothing in 

 common with the paleae afterwards possessed by the animal. 



So much for the spinous Annelidan larva from Trieste and 

 Nice and its genetic relations, which, I hope, have been pretty 

 correctly recognized. Let us now pass to another larva, also 

 discovered and described by Busch, which is figured on tab. 9. 

 figs. 1-8 of the work above quoted, and which has a great re- 

 semblance to the Mesotrocha sesc-oculata of the same observer. 



We have recently obtained information as to the origin of the 

 latter from Miiller (Monatsber. der Berl. Akad. 1854, p. 395). 

 We now know that it is the larva of the Chcetopterus Norvegiciis, 

 discovered by Sars. With this information we may probably 

 explain the second Mesotrocha, found by Busch at Trieste. It 

 may probably prove to be the larva of the Chcetoptei-us perga- 

 mentaceus {Triccelia variopedata, Ren.), found at Trieste, of which 

 I have given a more exact description in Wiegmann^s Archiv 

 for 1849, p. 340. On a previous occasion (Gott. Gel. x\nz. 

 1852, p. 857) I expressed the opinion that we might perhaps 

 suppose the Annelidan larvae of the Mesotrocha type to be the 

 descendants of a Serpula, or of some other worm in which the 

 segments of the anterior part of the body were distinguished, as 

 in Serpula, from the other segments by the form, structure and 

 position of the pedal tubercles; and, in fact, this supposition 



