570 MARY J. HOGUE 



podia are larger and more numerous than in the amoebae grown 

 on 2.5 per cent agar. 



When the amoebae of a 1.5 per cent medium are transferred 

 to a drop of tap water they immediately change shape. Slender 

 pointed pseudopodia (fig. 7) are sent out from all sides. These 

 are later withdrawn and a large anterior ectoplasmic pseudo- 

 podium formed. With this the animal advances as it did when 

 on agar, only here locomotion is more rapid. The pseudopodia 

 are merely feelers used while the amoebae is floating in the 

 water before settling on the slide or cover-glass. This process 

 has been fully described by Jennings ('04). 



From these experiments and drawings it seems evident that 

 the shape of the amoeba is dependent on the density of the me- 

 dium on which it is grown. Let us compare the work of Bur- 

 rows and Uhlenhuth with the present work and see whether their 

 explanation of the change in the shape of the growing tissue 

 cells will fit the case of the amoebae. 



Burrows ('13) finds that the cells move freely in thin media. 

 He explains this first by ''the better oxygen supply to the tissue 

 fragment and migrating cells. The increase in the supply of 

 oxygen to the tissue fragment is associated with an increase of 

 the metabolism of its cells and a greater production of repelling 

 tubstances. Second, the repelling substances diffuse in greater 

 concentration in the thin restricted areas of the medium." As 

 they diffuse through the medium they affect the shape of the 

 cells. Where they are most dense, i.e., near the old tissue, the 

 cells become contracted. As the posterior ends of the cells con- 

 tract the anterior ends flow out. 



Uhlenhuth ('15) has supplemented Burrows' theory by adding 

 that "the cell plasm in flowing out simply obeys the law of gravity 

 and this movement is initiated at the moment when the rela- 

 tion between the consistency of the medium and the consistency 

 of the cell plasm has attained a certain value, not yet ascertained, 

 brought about by the reduction of the firmness of the medium." 



In the case of the amoebae grown on a thin medium (0.5 per 

 cent agar) we must have this desired relation between the con- 

 sistency of the medium and the consistencj^ of the cell plasm. 



