412 F. H. Kreckor, 



fonner caii, of course, bc easily detected; cases of tlic latter are not 

 so readily foiind, nevert-lieless tlie freqiient occurrence of double or 

 elongating niicleoli are probably indications that amitosis does take 

 place. New cells are formed throughout tlie growing portion of the 

 iiitestine, most abundantly, however, at the tip and at a point some 

 distance anterior to it. The nuclei at the tip are iisually smaller and 

 cell division is rather freqiient. The other region of active prolifera- 

 tion is to be found at the base of the tongne, that is, where the new 

 part joins the old. Here quite a number of cells is to be found, espe- 

 cially at an early period when the entoderm is often considerably 

 thickened and occasionally a cell is to be seen in the j)rocess of division 

 (Fig. 7). Frequently instances of division were found as much as a Seg- 

 ment or more anterior to the regenerating region in parts of the intes- 

 tinal wall not inimediately affected by the wound. This has also been 

 observed by Iwanow in Lumhriculus. Where division was seen at such 

 a dista)ice it was always found to be mitotic, the axis of the spindle 

 Standing parallel to the longitudinal axis of the intestine. From the 

 fact that the proliferation of cells may occur in these more distant 

 parts it is evident that the elongation of the alimentary tract is not 

 dependent solely upon the formation of new tissue in the immediate 

 vicinity of the wound. In the region of greatest proliferation the 

 entoderm forms a disorganized group of cells but as growth proceeds 

 these become arranged in a single layer about a central cavity. These 

 cells are comparatively short in the transversa axis of the intestine 

 and somewhat attenuated antero-posteriorly but tlieir number in a 

 given area is practically equal to the number in a like area of the old 

 portion, the cliief difference being one of length. Cilia project from 

 the inner end of the cells at a very early period, in fact a fringe of cilia 

 is to be observed on the cells as soon as they have assumed a definite 

 Position in the intestinal wall. The process of growth once started 

 it proceeds ujiinterruptedly until the posterior end of the body wall is 

 reached. >Since the septa are not removed in the drawing out of the 

 intestine it might be supposed that they would grow across the open- 

 ings through wliich the intestine formerly passed and thus act as 

 an obstruction to the regeneration of the latter. This does not occur, 

 the apertures remain open and the intestine in its progress towards 

 the posterior end passes along through these openings. When regene- 

 ration is completed the intestine extends to the posterior end as a 

 straight tube v/hich is markedly narrower than the old portion. 



Before going further it might be well to con.sider briefly the ex- 



