GARY N. CALKINS. 



cutting, thus leaving no endoplasm exposed. In Stentor, Spiro- 

 stomum, Trachclocerca, Spathidium, Dileptns and Froutonia, the 

 walls come together in a relatively short time, but in Stylonychia 

 and Oxytricha, the union is delayed and sometimes never occurs. 

 In Paramecium, on the other hand, with the exception of the 

 fourth race mentioned above, the cut fragments form a new 

 im-mbrune upon the cut surface and the normal form is not re- 

 gained, the cell dividing asymmetrically. Where the vitality is 

 sufficiently strong for regeneration the normal form is occasionally 

 gained before division of the fragment, but more often after 

 a gradual change requiring several generations. In the fourth 

 race, on the other hand, the walls of the fragments behave exactly 

 as in Stentor or Lo.vopliyllnni and regeneration is perfect. 



The difference in regenerative power may be due to the dif- 

 ferences in potential at different periods of the life cycle, and 

 correlated with differences in the physical make-up of the proto- 

 plasm at such periods. This certainly appears to be the case 

 with the power to divide, abnormal divisions or monster forma- 

 tion taking place at the end of a long series of generations (see 

 Calkins, 1904), and in those races of Paramecium where regenera- 

 tion occurs in a small percentage of cases. 



Child and others have concluded that movements have much 

 to do with the restoration of form in regenerating animals. 

 Holmes shows that this is of secondary importance in the re- 

 generation of cut fragments of Loxophyttum. So too in Para- 

 mecinni, movement apparently plays no part whatsoever in the 

 restoration of form. The old peristome is always the site of the 

 new mouth formation, but in the majority of cases, if the mouth 

 is cut away, the anterior fragment with the bulk of the peristome 

 fails entirely to form a new mouth. The general shape of the 

 cell is usually retained; there is no rounding out of the cut frag- 

 inciit any more than there would be were the Paramecium made 

 of cheese. Form, therefore, is a highly stable characteristic of 

 Paramet i 'ni. This is demonstrated with remarkable clearness 

 in the case of UK Misters. A two mouth monster is, at first, little 

 more i han an elongate amorphous mass of protoplasm (Figs. 14, 

 [5, Jo). As it grow- older, however, the typical shape of the 

 mi-m begins to appear. Still more remarkable is the budding 



