of a few Annelids. 243 



haps what Quatrefages understands by Leucodora. At any rate 

 it is self-evident, from the following embryology of a species of 

 true Pohjdora, and of a species of what Claparede has called 

 Leucodora in his ' Beobachtungen/ that we have in each, deve- 

 loped at a very early period, genuine characters which refer un- 

 doubtedly one form to Pohjdora and the other to a different 

 genus [Leucodora, Clap., non Johnst.), probably Nerine, Johnst. 

 — thus proving the assertion of Quatrefages* of the generic dif- 

 ference between Leucodora, Clap., and Polydora, Bosc. And yet, 

 in spite of this generic difference, Claparede was correct in 

 maintaining the identity of Leucodora, Johnst., and Polydora, 

 Bosc, as can readily be seen on examining the descriptions and 

 figures of Boscf, Johnston, Oersted J, Leuckart§, Claparede, 

 and Keferstein ||. The error arises from Claparede^s mistaking 

 for the young of Pohjdora the young Annelids figured by him 

 on pi. 7 of his ' Beobachtungen,^ which, having no trace of the 

 characteristic fifth segment, belong therefore not to Polydora, 

 Bosc, but to some closely allied genus, as suggested above. It 

 is not probable that such an accurate observer as Claparede would 

 have overlooked this segment, so prominent in the youngest 

 specimens of our Polydora, as well as the presence of the 

 glands, so early developed in the young worm, and which he 

 noticed in his description of the adult in Miiller's ^ Archiv.' In 

 my earlier observations I made a similar mistake between the 

 young of Polydora and Nerine; and it was not till the striking 

 difference of the fifth ring and the presence of glands were no- 

 ticed that I could afterwards always readily distinguish the 

 young of these two genera, so easily mistaken at first sight. 



I shall introduce a few of the stages of Nerine, with a short 

 description of the adult, for the sake of comparing them with 

 the different stages of Pohjdora, which will be given more in 

 detail, and of identifying them, as far as possible, with those 

 observed by Claparede. It is apparent at the first glance, on 

 comparing his drawings of Leucodora with those here given of 

 Nerine and Polydora, that they represent closely allied genera; 

 but, as similar young stages of other genera have also been 

 figured by Leuckart and Tagenstecher as Spio, as well as by 



* " Note sur la Classification des Annelides, et reponse aux observations 

 (le M. Claparede," in Ann. des So. Nat. 5"= ser. iii. 1865 (Annals, ser. 3. 

 vol. xvii. p. 107). 



t Histoire Naturelle des Vers. 



X ** Zur Classification der Anneliden," in Archiv fiir Naturg. 1844, i. 

 p. 105. 



§ " Zur Kenntniss der Fauna von Island," in Archiv f. Naturg. 1849, 

 i. p. 200. 



II " Untcrsuchungen iibcr nicdere Seethiere," in Zeits. f. wiss. Zool. 

 xii. p. IIG. June isr.2. 



