NEREIS. 151 



plied figures exhibiting still other dissimilitudes, but the pattern, 

 though modified, is always essentially the same. Some of these 

 differences proceed from selecting feet of non-corresponding seg- 

 ments ; others are produced by differences in the condition of the 

 worm when killed, — for example, from its being filled with ova or 

 not ; and others again from a difference in the strength of the spirits 

 in which the specimens are placed. In some specimens which had 

 been long preserved, the post-occipital segment was scarcely larger 

 than the one behind ; but when alive, the great proportional size of 

 the former is always very obvious. 



I cannot refer N. lyelagica to any of the species described by Au- 

 douin and Milne-Edwards. From their description and figure of 

 N. Beaucoudrayi, it is evidently nearly allied ; but N. Beaucoudrayi 

 differs in having only 100 segments, while it is equal or superior 

 in size ; in the first ring not being larger than the following ; and 

 in the greater elongation of the tentacular cirri. 



(«) Bell Rock, Scotland, Dr. Leach. 



{b) Devonshire Coast, Dr. Leach. 



(e) Holy Island, Dr. Johnston. 



(d) Holy Island, Dr. Johnston. 



(e) Holy Island, Dr. Johnston. 



Plate XV. Fig. 1 . Nereis pelagica of the natural size. 1 a. The head 

 and proboscis magnified (see also p. 145). \b. A. lateral view of a 

 foot. 1 c. Two bristles. 2. The young? of N. pelagica. 



The changes which the Annelides pass through, from the egg 

 state to their maturity, have not been traced by any one*, and the 

 general belief appears to be that none of the class undergoes any 

 metamorphosis, proceeding from the egg with all the characters and 

 lineaments of the parents. I have no direct observation to oppose 

 to this belief, which, however, I have been led to think is question- 

 able. In PI. XV. fig. 2 represents what seems to me to be the young 

 of a Nereis, probably of N. lielagica, and the differences between it 

 and the adult are not inconsiderable f. The tentacula and tenta- 

 cular cirri, it will be observed, are wanting, while the head is large 



* The evolution of the egg in the Annelides has been very carefully traced by 

 De Quatrefages, and the various phases of it admirably described in his " Memoire 

 sur I'Embryogenie des Annelides " in the Annales des Sciences naturelles for 1848, 

 vol. X. p. 153, &c. In vol. viii. p. 99 of the same excellent journal, there is an in- 

 teresting " Note sur rEmbryogcnie des Annelides " by the same author ; see also 

 torn. iii. p. 142 (1845). But these essays are certainly not superior in interest 

 to M. Milne-Edwards's " Observations sur le Developpement des Annelides " in 

 torn. iii. p. 145 (1845). This is written in Edwards's usual style, — characterized 

 by elegance, copiousness, and ease. 



t From the discoveries of M.-Edwards, it seems likely that I am wrong In this 

 conclusion. The larva of a nearly allied species does not exhibit the lobes at the 

 sides of the head, &c. See the figures of M. Edwards in Ann. des So. nat. iii. 

 pi. 10 & 11 (1845). See also Williams, Rep. Brit. Assoc, p. 166; Quatrefages, 

 Souvenirs, ii. p. 45 ; Kay Soc. Rep. 1845 ; Peach in Ann. & Mag. Nat. Hist. ser. 2. 

 viii. p. 500. pi. 17. figs. 5, 6. 



Does Peach's worm belong to the genus Dujardinea .' See Ann. & Mag. Nat. 

 Hist. xiv. pp. 32, 33. 



