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. pelagica to any of the species described by Au- 

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

 N. Beaucoudrayiy 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. 



(a) Bell Rock, Scotland, Dr. Leach. 



(jb) Devonshire Coast, Dr. Leach. 



(c) Ploly 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). lb. 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. pelagica, 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 " Meraoire 

 sur TEmbryogenie 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 I'Embryogeuie des Annelides " by the same author ; see also 

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

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

 tom. 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 Sc. nat. iii. 

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

 Souvenirs, ii. p. 45 ; Ray 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. 



