2IO 



DYNAMICS OF LIVING MATTER 



longitudinal elements to which reference was just made. If a lateral 

 incision be made in the body at c, not too far from the openings, ocelli 

 will be formed at each free end of these elements. Here the longi- 

 tudinal elements show heteromorphosis, inasmuch as they are capable 

 of forming ocelli at both ends. 



I am inclined to believe that in each of these cases the individual 

 longitudinal element represents a conductor for nutritive material or 

 specific morphogenic substances in the sense of Sachs. It must remain 

 undecided for the present whether this flow occurs through the hollow 

 space' or through the tissue or certain cells of the tissue. 



4. REGENERATION AND HETEROMORPHOSIS IN FRESH-WATER 



PLANARIANS 



It had been known for a long time that if the head and the tail be 



cut off from a fresh-water Planarian, at the front end a new normal 



head, at the back end a new tail, will be 

 regenerated (Fig. 49). Morgan* made the 

 interesting observation that if a piece acdf 

 be cut obliquely (Fig. 50) instead of at right 

 angles to the 

 V longitudinal 

 axis from a 



FIG. 49. AFTER MORGAN. Planarian, a 



tiny head is 



formed at the foremost corner of the piece 



a and a tiny tail at the hindmost corner /, 



Fig. 51. Why is it that in the oblique 



piece the head is formed in the corner 



and not all along the cut surface as is the 



case when the cut is made at right angles 



to the longitudinal axis? I am inclined 



to believe that the right answer to this 



question has been given by Bardeen.f 



Bardeen has pointed out the apparent role 



that the circulatory (or so-called digestive) 



canals in Planarians play in the locali- 

 zation of the phenomena of regeneration, inasmuch as the new head 



always forms symmetrically at the opening of the circulatory vessel 



* Morgan, Regeneration, New York, 1901. 



t Bardeen, Am. Jour. Physiology, Vol. 5, p. I, 1901 ; and Archiv fur Entwickelungs- 

 mechanik, Vol. 16, p. i, 1903. 



FIG. 50. AFTER MORGAN. 



