336 STUDIES IN GENERAL PHYSIOLOGY 



ther insight into the nature of these ultimate elements will 

 consequently be dependent upon a knowledge of this order. 



This significance of the quantity of living substance as 

 the carrier of a definite amount of energy is also apparent 

 in the regeneration of multicellular animals. According to 

 the experiments of Nussbaum, "at least one ectoderm, one 

 entoderm, and one cell from the intermediary germinal layer 

 is necessary" for the regeneration of a Hydra capable of 

 reproduction. 1 But this minimum gives us only a qualita- 

 tive limit, in so far as the three qualitatively different ele- 

 ments are necessary. So far as the quantity is concerned, 

 it must be said that a very large multiple of each of these 

 three elements is necessary for regeneration. In experi- 

 ments on Tubularia which Miss Bickford made in my labo- 

 ratory two years ago 2 it was found that pieces 1 mm. long 

 from the stem of this Hydroid are no longer able to regener- 

 ate into complete Tubularise; either only a simple polyp 

 without stem and root is formed, or a peculiar heteromor- 

 phous formation, a sort of Janus head, occurs, consisting of 

 two polyps connected with each other by their aboral ends, 

 while the stem and root are missing between them. 



That the smallest amount of matter capable of develop- 

 ment must have a different absolute size in different organ- 

 isms that, for example, it must be smaller for a coccus 

 than for an Arbacia egg need not be specially mentioned. 



10. The results of our observations are briefly as follows : 



a) The limits of divisibility of living matter must vary 

 according to the character of the life-phenomena used as 

 a criterion of life. Each quantity of living matter is the 

 bearer of a definite quantity of energy. 



6) The smallest fraction of an unsegmented egg of 

 Arbacia necessary for the formation of a pluteus is about 



1 Archiv filr mikroskopische Anatomic, Vol. XXXV (1890). 



2 E. BICKFOKD, Journal of Morphology, 1894. 



