INTRODUCTION 23 



theoretical grounds, it does not exist, while from another standpoint 

 it is insoluble. If one be asked to divide living things into two distinct 

 groups of which the one contains only animals, the other only plants, 

 the question is meaningless, for plants and animals are concepts 

 which have no objective reality, and in nature there are only indi- 

 viduals. If, in considering those forms which we regard as true 

 animals and plants, we look for their phylogenetic history, and decide 

 to place all of their allies in one or the other group, we are sure to 

 reach no result ; such attempts have always been fruitless." 1 



No one at the present time denies the extremely close relation 

 which Huxley ('76) has so clearly pointed out between the lower 

 algae and some of the flagellates, and it is the general opinion that no 

 one feature separates the lowest plants from the lowest animals, and 

 the difficulty — in many cases the impossibility — of distinguishing 

 between them is clearly recognized. Curiously enough, this modern 

 idea was early expressed by Buff on at the time when Aristotle's view 

 of the plant-like nature of some animals (Zoophyta) was still accepted 

 in regard to the Ccelenterata. Buff on wrote as follows in 1749: 

 " From this investigation we are led to conclude that there is no 

 absolute and essential distinction between the animal and vegetable 

 kingdoms; but that Nature proceeds from the most perfect to the 

 most imperfect animal, and from that to the vegetable." This state- 

 ment might have been written in 1899, but Buff on unfortunately goes 

 on to say : " Hence the fresh-water polypus {Hydra) may be regarded 

 as the last of animals and the first of plants." 2 



Ehrenberg included a large number of plant forms among his 

 Infusoria, most of which Dujardin threw out, restricting the group, 

 practically, to the Protozoa as known to-day. But the discovery of 

 flagellated swarm-spores of algae cast doubt on the animal nature of 

 the organisms which Dujardin had described as flagellates. Von 

 Siebold ('45) was thus led to retain only the families Astasiidse and 

 the Peridinidse in his zoology, removing the Mastigophora, as a group, 

 to the botanical side. In this he was followed by Bergmann and 

 Leuckart ('56), while Cienkowsky ('65) placed them as an intermediate 

 group between animals and plants. Others went to the opposite 

 extreme and actually excluded the algal swarm-spores from the plants, 

 on the ground that they were merely flagellated parasites living on the 

 plant-cells (Diesing, '65). Still others, noting that some of the flagel- 

 lates are animal and some vegetable in their nature, undertook the 

 impossible task of finding a single distinguishing character. The 

 presence of green coloring matter or chlorophyl, upheld by Cohn ('76) 

 and others as a characteristic vegetable feature, seemed to be a good 



1 C'9 6 ). P- 5 l8 - 2 Edition 1812, p. 357. 



