130 LIBBIE H, HYMAN 



S. Regeneration in Dero limosa 



While many investigators have stated that the naids possess 

 high capacity for regeneration, yet I have l)een unable to find 

 any very dehnite data on the physiological aspects of regener- 

 ation in these forms, and no data at all on Dero limosa. Most 

 of the regenerative studies on naids have been histological, and 

 have concerned themselves with the germ layer hypothesis, and 

 are, therefore, of little value from the present physiological 

 point of view. 



In working on regeneration, I have usually followed the simple 

 method of cutting the worms up into a series of equal pieces 

 along the axis, as fourths, eighths, sixteenths, etc. In this way, 

 one discovers at once the effect of difference in size, and regional 

 differences. A number of worms are cut up at once, and all the 

 pieces of the same level put together. The pieces are kept in 

 large stender dishes or finger bowls, in filtered water, which is 

 changed occasionally. It is not necessary to add any debris 

 except in the case of the naids, where the presence of a small 

 amount of the cultural material seems to reduce the mortality, 

 although it makes the finding of the pieces difficult. 



Dero limosa possesses high regenerative capacity. If these 

 worms are cut up into two, three, or four equal pieces along the 

 axis, each piece regenerates a complete anterior and posterior 

 end, with practically no mortality. A complete anterior end 

 is the head of five segments with brain, mouth, prostomium, 

 pharynx, and four sets of setae; a complete posterior end con- 

 sists of the anal segment with its expanded gill and pavilion, 

 four ciliated gills, and in front of this a variable number of new 

 segments. The new tissue is always readily distinguishable 

 from the old for a considerable length of time, by its lighter color, 

 for it takes some time for the dark granules to accumulate in the 

 chloragogue cells. 



With shorter pieces, sixths or eighths — it is not practicable to 

 cut pieces shorter than this in Dero, — there is considerable 

 mortality, so that it is difficult to secure constant results. The 

 anterior piece, containing the head, does not regenerate poste- 



