RELATIVE STABILITY OF LIVING MATTER 327 



4. It may be unlike any normal structure of the body, as when 

 a new leg is " unlike any other leg on the body" 1 (neomorphosis). 



With respect to the tissues from which regenerated parts arise 

 two distinct cases are to be noted : 



1. Where the part regenerated springs from tissue of the 

 same kind, requiring only an extension of growth, as when an 

 injured muscle is repaired. 



2. Where the regenerated part springs from tissue of a totally 

 different order, as where a severed leg is restored from the cut 

 outward, or where the lens of an eye arises from the iris, re- 

 quiring differentiation as well as growth. 2 This subject will be 

 pursued further under the section on " Origin of New Cells and 

 Tissues." 



Effect of temperature upon regeneration. 3 Planarians were cut 

 in two transversely at the pharynx. No regeneration took place 

 below 3 C. Of six specimens kept at this temperature only 

 one regenerated, and that incompletely, the eyes and brain 

 being incomplete after six months. The temperature at which 

 regeneration took place most rapidly was 29.7, at which a new 

 head formed in four and six-tenths days. At 31.5 it required 

 eight and a half days to complete the head ; at 32 regeneration 

 commenced, but death occurred in about six days; at 33 re- 

 generation was slight, and at 34 none took place, death occur- 

 ring within three days. Other species showed a similar range 

 for optimum, minimum, and maximum. 4 



Influence of food upon regeneration. 5 While regeneration takes 

 place more rapidly with a full food supply, it nevertheless pro- 

 ceeds without it. In this case the new growth appears to be de- 

 rived not from surplus food material but from the protoplasm 

 itself, resulting in reduction in size. 



If a planarian be kept for several months without food, in 

 this starved condition it gradually shrinks in size, even to one 

 thirteenth of the normal (see Fig. 40). 



If a starved worm be cut in two pieces, each will regenerate, 

 though more slowly than if fed, the new part increasing in size 

 at the expense of the old. 



1 Morgan, Regeneration, p. 24. 3 Ibid. pp. 26-27. 5 Ibid. pp. 27-29. 



2 Ibid. p. 205. 4 Ibid. pp. 26-27. 



