CHANGE OF SHAPE IN PLANARIA. 



28 5 



lines. Figs. 17 and 18 indicate this change in shape of the chro- 

 matophores in the region posterior to a new head, and Figs. 19 

 and 20 for a region anterior to a new tail. In the pieces in alco- 

 hol and ether this change in shape of the chromatophores appears 

 only when the change in shape occurs, not when the new tissue 

 is formed. In cases where the change of shape is inhibited in the 

 anaesthetic (Figs. 2, 4, 9, 12) it does not appear at all, but if such 

 pieces are returned to water, and the change of shape occurs, the 

 stretching of the chromatophores also appears. In Fig. 14, for 

 example, it did not appear so long as the piece was kept in the 

 ether, but after several days in water it was most conspicuous in 

 the slender anterior region (Fig. I 5), this region appearing almost 





FIGS. 17-20. 



as if finely striped in the longitudinal direction. This change in 

 shape of the chromatophores is actually a stretching, not a migra- 

 tion, for it is possible to select some particular spot which happens 

 to be conspicuous for some reason and to observe its change of 

 shape from day to day : in such cases it can be seen clearly that 

 merely elongation not migration occurs. 



A similar elongation is visible in the parenchyme cells in sec- 

 tion. Stevens ('07) has recently described this elongation or 

 orientation of the parenchyme cells and regards it as indicating 

 migration, but Steinmann ('08) does not agree with her. As a 

 matter of fact the specimens in which the change of shape is 

 inhibited by anaesthetics show nothing of the sort even in regions 

 adjoining those where new tissue is being formed, but if such 

 pieces be returned to water the cells of the parenchyme become 

 very distinctly elongated or oriented in the direction in which 

 elongation of the body is occurring, even though no new tissue 

 is being formed at the time. In short the change in shape or 



