REPRODUCTION OF LOST PARTS. 127 



A more advanced condition of the head is found after two or three months (Plate XXII, 

 fig. 10). The snout is very much elongated both before and behind the commissures. In some 

 eye-specks now appear in their usual position, and there is a distinct channel leading inwards to 

 the enlarged proboscis ; the ganglia approach the normal shape, and the cephalic pits, with their 

 ducts passing into the posterior end of the cephalic fissures, are well marked. The anterior part 

 of the alimentary tract has assumed a rounded form behind the ganglia, with the mouth (w) 

 in the usual position. In those best developed {e.g. Plate XXII, fig. 11), the first or oesopha- 

 geal division of the canal is differentiated from the succeeding portion; and in the ordinary 

 fragments it is apparent that the former consists, for the most part, of new texture. Such 

 examples, however, do not always possess eye-specks. The circulation now scarcely differs from 

 that in the adult. 



The motions of those with reproduced heads (Plate XXII, fig. 11) are not so active as 

 usual in young Linei, and the animals are at once distinguished by the pointed nature and pallor 

 of their snouts. 



The formation of a complete individual, and the prolonged retention of certain functions by 

 the headless fragments, under circumstances so adverse as the above, may give some idea of the 

 powers of regeneration and vitality possessed by these worms in their native haunts ; for it is to 

 be remembered that they were at a great distance from the sea-coast, had no food (except what 

 they might obtain from microscopic animals or the fragments of their own bodies), and had a 

 very limited supply of salt water. 



Moreover, besides the application of the ordinary laws of natural and sexual selection (if 

 such exist in these forms), we have thus the additional (fissiparous) operation by which mere 

 fragments of the body of the animal are capable of reproducing the entire organism and all its 

 complex parts. 



In like manner very serious wounds made in removing the proboscis are easily repaired, 

 without leaving a trace of the injury after the pigment is fully developed in the cicatrix. Portions 

 may also be removed from the posterior end of long species for microscopic purposes, while the 

 rest of the animal lives and thrives for further observations. 



The reproduction of the proboscis is referred to under the anatomy of that organ in the 

 Enopla. 



Comparatively few abnormalities of external form are met with in the Nemerteans. An 

 example of Lineus sanguineus, found at Lochmaddy, had a curious diverticulum about the 

 posterior end of the oesophageal region. This process was covered by all the coats of the body, 

 and, in the preparation, contained a knuckle of the proboscis. The accompanying woodcut 

 (fig. 8) represents the anterior part of the specimen during life. 



Pig. 8. 



Lineus sanguineus, with a diverticulum of the body. Somewhat enlarged. 



