248 REPORT— 1851. 



plete separation is effected and the j'oung animal thenceforth leads an inde- 

 pendent life. Not unfrequently, however, before its detachment, a new set 

 of segments is developed in front of it, which in like manner is provided with 

 a head and separated from the main body by a partial constriction ; and the 

 same process may be repeated a second and even a third time ; so that we may 

 have in this animal the extraordinary phsenomenon of four worms which are 

 afterwards to exist as separate individuals, united end to end, receiving 

 nourishment by one mouth and possessing one anal orifice. A similar phse- 

 nomenon has been observed in several genera of the dorsibranchiate order ; 

 but the gemniEe thus detached are not complete individuals, for each con- 

 sists of little else than a generative apparatus, with the addition of locomo- 

 tive organs ; thus bearing a similar rehition to the parent stock, which does 

 not form generative organs of its own, to that which is borne by the Medusae- 

 buds to the Polype-stock. 



"In the one case, as in the other, it must be improper to reckon the gene- 

 rative segments of a new generation, since they are merely the ' complements' 

 of the organism that would be incomplete without them. 



" As many as six of these generative offsets have been seen in continuity 

 with each other, and with the parent stock, by Prof. Milne-Edwards, the 

 most posterior being evidently the oldest, and one in direct connection with 

 the parent, consisting an yet but of a few segments and being obviously the 

 youngest. A similar detachment of a generative segment has been observed 

 among the Tubicolce. There are several Annelids which may be multiplied 

 by artificial sub-division, each part being able to grow up into the likeness 

 of the perfect animal, though they do not spontaneously reproduce them- 

 selves in this mode*." 



The whole of this subject is not easy of proof; experiments conclusively 

 ai)d unexceptionably conducted must extend over a considerable time, and 

 should be followed out under the most favourable circumstances of leisure 

 and opportunity ; a very large portion of the subject may, however, even with 

 our present acquaintance with the habits of the Annelida, be very confidently 

 disposed of. 1st, as to the spontanemis division of the body. — It is true that 

 towards the latter end of every summer two species of worms are multiplied 

 by a cutting across of the body at one or more points. If the fission occurs 

 at more than one point, the animal becomes of course divided into more than 

 two pieces. This circumstance seldom occurs. The fission in Arenicola 

 generally occurs somewhere within the middle third of the body, securing a 

 few branchial tufts for each fragment. The tail however is sometimes de- 

 tached, and sometimes the division happens very near the head. This pro- 

 cess, both in Nois and Arenicola, happens during July and August. The 

 cephalic and caudal pieces in Arenicola continue for some time to writhe in 

 the S'and, somewhat further down in the soil from the surface than the per- 

 fect individuals. Towards September, the fragments, both that attached to 

 the head and that belonging to the tail, dissolve away ring by ring, and 

 finally disappear by decomposition. If the fragment examined be that of 

 the tail, it will be observed, at the point of separation, to exhibit an eversion 

 of the edges, placing the alimentary canal exteriorly ; and a very evident in- 

 crease of size in the vessels also occurs, accompanied by a tumified state of 

 all the structures of the part. From this latter fact it is easy to be misled 

 into the idea that the vessels can become enlarged for no other purpose than 

 that of repairing the injury done by the fission, or perchance of reproducing 

 the part detached by that process. Such would naturally be the meaning 

 which a physiologist would attach to the swollen appearance of the blood- 

 * Carpenter's Principles of Physiology, 3rd ed. p. 934, par. 714 a. 



