126 EEPKODUCTION OF LOST PARTS. 



occasionally tapered. One of the most interesting features was the gradual development and 

 elaboration of the products of the generative organs (in this case the male elements) in the 

 headless fragments, so that when in February they were placed in clean sea-water, some gave exit 

 to milky clouds of perfect spermatozoa. This would seem in these animals to be the main aim 

 of such a provision, since their very length and softness, if not fragility, apparently court dis- 

 severance. They display greater vitality in this respect than the majority of the Annelida, and 

 it is not necessary that the sea-water be changed for years, or that fragments of their own bodies 

 or other debris be present. In one species, moreover, each of the numerous fragments into 

 which its lengthened and fragile body breaks becomes a perfect animal. 



In captivity, specimens of Lineus sanguineus (Plate V, fig. 2) have often a great tendency to 

 rupture into many pieces. These fragments lie on the bottom of the vessel, and, in the majority, 

 consist of the body-wall, its nerve-cords and vessels, the central alimentary chamber, and the dorsal 

 sheath for the proboscis. Numerous parasitic gregariniform bodies, as well as the peculiar ova to 

 be described subsequently, 1 may also be seen in them ; and the new animals are thus supplied, ab 

 initio, with such structures in their digestive tracts, without being subjected to the earlier stages 

 in their development. For some time after separation the large aperture of the digestive 

 chamber existing at each end remains closed by firm contraction of the circular muscular fibres 

 of the body- wall; but by-and-by new cell-growth occurs at both extremities, especially the 

 anterior. At the latter the parts firmly contracted by the primary muscular spasm gradu- 

 ally become more or less consolidated by a cicatrix. This new growth steadily increases 

 in bulk, distinguishing the anterior end of the fragment, even in the early stages, by its con- 

 spicuous pallor. The appearance of this extremity in a specimen, probably about three weeks 

 after rupture, is shown in Plate XXII, fig. 7. The head is represented by the pale, sprouting 

 mass in front of the alimentary tract, and there is no further differentiation of organs than the 

 separation of the exterior (cutaneous) elements from the inner mass, and the ciliated aperture 

 (a) leading into the sheath for the proboscis. The three contractile circulatory channels of the 

 body course forward to the pale developing region, and apparently communicate with each other 

 without passing into it ; they are connected by the usual transverse branches throughout their 

 course. The posterior end of the fragment shoots into a conical tail (Plate XXII, fig. 8), with a 

 well-formed anus (z) in its proper position, and through which, under pressure, a prolapsus of 

 the wall of the digestive chamber occasionally occurs, or an escape of one or more gregariniform 

 parasites. 



In the next stage (Plate XXII, fig. 9) the anterior end has assumed a more conical form, 

 and there is a greater differentiation of organs. The cutaneous elements are distinctly marked, 

 and a miniature proboscis (a) occupies its sheath, both springing from a point some distance 

 behind the tip of the snout, and corresponding to the commissure of the developing ganglia (h), 

 which latter, however, are scarcely apparent. The proboscidian sheath contains a clear fluid and 

 granules, which now and then distend the front as in the figure. The proboscis (a) is quite 

 free posteriorly. The cephalic fissures are indicated on each side by slight superficial grooves, 

 very strongly ciliated. Besides the faint contour of the ganglia, which spring from the anterior 

 ends of the nerve-trunks, the cephalic pits and glands (m) are outlined. The circulation 

 in the vessels extends only to the posterior border of the white snout. The digestive tract 

 presents no subdivision into regions. 



1 See also ' Journ. of Micros. Science/ 1867, " Trans. Micros. Soc," p. 40. 



