EXTERNAL FACTORS OF REGENERATION IN ANIMALS 27 



regeneration was slower, requiring 8.5 days to make a new head. At 

 32 C. incomplete regeneration sometimes took place, but death 

 occurred in about six days. At 33 C. regeneration was very slight, 

 and the animals died within three days. At 34 C., and above this 

 point, no regeneration took place, and death soon occurred. 



In Hydra viridis, Peebles ('98) has found that regeneration is 

 quicker at 26-27 C. than at 28-3O C. At the former temperature 

 regeneration takes place in 48 hours. If kept at I2C. pieces may 

 regenerate in 96 hours, but not all the pieces had regenerated in this 

 case until 168 hours. 



INFLUENCE OF FOOD ON REGENERATION 



While the growth of an animal or of a plant is, in most cases, and, 

 of course, within certain limits, directly connected with the amount 

 of food that is obtainable, nevertheless extensive regeneration may take 

 place in an animal, or part of an animal, entirely deprived of food. In 

 this case the material for the new part is derived from the excess of 

 material in the old part, and not only surplus 

 food material, but even the protoplasm itself 

 appears to be drawn upon to furnish material 

 to the new part. The relation between regen- 

 eration and the amount of food present in the 

 old part is well shown by experiments with 

 planarians. If a planarian is kept for several 

 months without food, it will decrease very 

 much in size. In fact, the volume of a 

 starved worm of Planaria Ingubris compared 

 with that of a fully fed individual may be only 

 one-thirteenth of the latter (Fig. 13, A, B\ 

 If a starved worm is cut in two pieces, 

 each piece will regenerate, although less 

 quickly than in a well-fed worm. The new 



part will continue to increase in size at the FIG. 13. Drawn by N. M. 

 expense of the old piece that is already in a 

 starved condition. On the other hand, an 

 excess of food does not necessarily produce a 

 hastening of the regeneration, for, as Bardeen 

 ('oi) has shown, worms that have been for several days without food 

 may regenerate more quickly than worms that have been fed just 

 before they were cut into pieces. 



The growth of the new part at the expense of the old tissues is a 

 phenomenon of the greatest importance, an explanation of which 

 will involve, I think, the most fundamental questions pertaining to 



lugubris. B. Same after 

 being kept without food 

 for 4 mos. 13 days. Both 

 drawn to same scale. 



