ORGANIC DIFFERENTIATION 79 



but in spite of this they conserve a large measure of 

 individuality. It has always been known that certain parts of 

 a plant could be separated from the plant itself without dying, 

 and that if placed in propitious conditions could subsequently 

 give birth to a new plant. As early as 1740-4 1 Trembley 

 showed that the freshwater Hydra could be dismembered in 

 a similar manner, and since then it has been discovered that 

 sponges, polyps, and all ramiform organisms possess this 

 property. Transplantation of tissues and grafting have even 

 succeeded as completely with the higher animals as with plants, 

 and within recent times Dr. Alexis Carrel has succeeded in 

 maintaining life and promoting growth in pieces of connective 

 tissue, even nerves, under proper artificial conditions, without 

 the aid of any organism. 2 This directly proves the independence 

 of anatomical units as Claude Bernard had deduced from his 

 physiological experiments. 



This independence still appears in the course of embryo- 

 genetic development. The first phases of this development 

 consist in division of the egg into two elements, then four, eight, 

 etc., all of which are quite alike as long as the egg does not 

 contain a large quantity of nutritive material and as long as 

 they are not so numerous as to necessitate an arrangement into 

 superposed layers. These units are called blastomeres. They 

 resemble the egg itself. Certain eggs, when violently shaken, 

 divide into the two original blastomeres, and each one of them 

 develops independently and produces an embryo differing 

 from the normal one only in being half its size. 3 



Such a separation of blastomeres can take place 

 spontaneously but accidentally, even in man. The egg then 

 develops two exact counterparts, always of the same sex, and 

 in the case of the mammals, possessing only one placenta. 

 What is purely accidental in man is of normal occurrence 

 among such mammals as the armadillos, the carapaced 

 Edentata of South America. The egg of the nine-banded 

 Armadillo always divides in such a manner as to produce four 

 of a sex at the same time ; 4 and that of the hybrid Armadillo 



1 XXVIII. 



2 XXIX. 



3 Driesch (XXX) experimented thus on the eggs of the Sea-urchin and 

 of A mphioxus, and Bataillon (XXXI) has done the same for the Lamprey. 



4 De Morgan, XXXII, for a highly specialized fish belonging to the 

 Malacopterygii. 



