Regc?7eration in Polychoerus Caudatus. 345 



oldest stages, but in a few of these, the growth of new material 

 between the united edges can be seen in section. (Fig. 13, v.) 

 By studying the whole series of sections, this region can be identi- 

 fied as the place where the cut edges united. The accumula- 

 tion of nuclei shows new tissue to be regenerating on both sides of 

 the line of union. 



A few cases of lateral regeneration were studied, but the sec- 

 tions showed no divergence from anterior and posterior regenera- 

 tion. 



The regeneration of Polychoerus caudatus is an excellent 

 example of the remolding of the old tissue in a piece of an organ- 

 ism, into the tissues and form of the whole organism, without the 

 assistance of cell division by mitosis or amitosis. This is what 

 Morgan calls morphallaxis. Other flatworms in which regenera- 

 tion has been worked out histologically, Planaria simplicissima 

 and Planaria maculata, show a proliferation of new cells at the 

 cut end, as well as the changes of form due to morphallaxis, but 

 in Polychoerus the new part is formed wholly of cells which migrate 

 from the old part. Regeneration in this form is, therefore, an 

 example of morphallaxis, pure and simple. 



Bryn Mawr College, Pa. 

 April 19, 1905. 



LITERATURE. 



Bardeen, C. R., '01. — On the Physiology of Planaria maculata with Especial 



Reference to the Phenomena of Regeneration. Am. journ. of 



Physiology, vol. v, 1901. 

 Child, C. M., '04a. — Studies on Regulation. IV. Some Experimental Modifica- 

 tions of Form Regulation in Leptoplana. The journal of Exp. 



Zoology, vol. I, No. I, 1904. 

 '04b. — Studies in Regulation. V. The Relation between the Central 



Nervous System and Regeneration in Leptoplana: Posterior 



Regeneration. Ibid., No. 3, 1904. 

 '04c. — Studies in Regulation. VL The Relation between the Central 



Nervous System and Regulation in Leptoplana: Anterior and 



Lateral Regeneration. Ibid., No. 4, 1904. 

 Curtis, W. C, '02. — Life History, Normal Fission, and Reproductive Organs of 



Planaria maculata. Proc. Boston Soc. of Nat. Hist., vol. xxx. 



No. 7, 1902. 



