Some Phenomena of Regeneration in Lininodrilus and related Forms. 423 



whether or not the injiiry had any effect in tliis case. How far frora 

 tlie point at which the animal had been injured the neoblasts were 

 affected could not be deterrained with certainty. Neoblasts were seen 

 luigrating along the nerve as many as seven somites anterior to the 

 woiind, but it was not possible to teil how many somites they had al- 

 ready traversed. 



Either after they have reached the end of the nerve or during the 

 journey the neoblasts begin to enlarge so that they frequently attain 

 a gigantic size. When once they arrive at their destination they Cluster 

 about the nerve cord and later, as their number increases either by 

 division or by the arrival of others, they move laterally from the nerve 

 and also somewhat dorsally, in advanced stages some being present 

 half way to the dorsal side or slightly farther (Fig. 12 and 15). The 

 more peripherial neoblasts attach themselves to the body wall by means 

 of short pseudopodia (Fig. 12). In what raay be termed the resting 

 stage on the septa, before migration, the neoblasts are usually in a more 

 flattened condition than is here the case, a greater surface being applied 

 tu the septum than is now applied to the body wall. Meanwhile the 

 body wall in the region opposite the neoblasts has elongated so that 

 the nerve which was originally in contact with the cut surface of the 

 body wall is now quite a distance from the end of the body and the 

 neoblasts, which have been actively dividing the while, form a compact 

 mass filling all the ventral half of the coelom posterior to the point 

 where the nerve ends. The mass does not extend quite to the anal 

 opening but stops a short distance in front of it. It is at such stage 

 as this that the line of demarcation between the neoblasts and the 

 ectoderm is most difficult to distinguish (Fig. 13). The neoblasts 

 -il^ng the midventral line are not in such an active State of division 

 as are those along the sides and of the latter cells those nearest the 

 posterior end of the body are the largest. These larger cells give rise 

 to the smaller cells which compose the greater part of the mass. Iwanow 

 has suggested that this condition is comparable to the division of the 

 neoblasts i. e. teloblasts in the embryonic stages. 



The cells resulting from the division of these neoblasts are spindle 

 shaped and overlap each other thus becoming more or less arranged 

 into a series of approximately parallel columns at right angles to the 

 intestine and the body wall (Fig. 13 and 14). These columns are the 

 primordia of the septa. The forniation of the septa proceeds in a 

 antero-posterior direction, the posterior columns being less differen- 

 tiated than those farther forward. The more anterior columns, keeping 



