S68 The Unity of the Organiftm 



the preface to the monumental Treatise on Comparative 

 Embryology by F. M. Balfour contains this: ". . . the 

 work is, I believe, with the exception of a small but useful 

 volume by Packard, the first attempt to deal in a complete 

 manner with the whole science of Embryology in its recent 

 aspects. . . ." ^^ But the introduction tells us specifically 

 that the actual scope of the work is not to be thus ambi- 

 tious after alL "The present treatise deals only with the 

 Embryology of Animals, and is further confined to those 

 animals known as Metazoa." ^^ It will be noted that noth- 

 ing in this statement compels the inference that Balfour con- 

 ceived Embryology as being actually limited to the metazoa. 

 In fact, if anything, the opposite might be inferred. Con- 

 siderable reference is made to protozoan reproduction in the 

 Introduction, which however has to do only with conjuga- 

 tion and spore formation and the problem of the origin 

 of the metazoa from the protozoa and especially the origin 

 of sexual reproduction. But the theory of the "formation 

 of the individual from the structureless germ'' (italics 

 mine),^^ and of the individual metazoan as "equivalent to 

 a number of Protozoa coalesced to form a single organism 

 in a higher state of aggregation," '^'^ advnnbrates the fal- 

 lacious doctrines about the relation of the organism's cells 

 to the organism which have come to dominate biological 

 theory, and against which we are taking strong ground. 



"Inasmuch as the individual Protozoan has the morpho- 

 logical value of a single cell, the embryology of the Protozoa 

 belongs to the province of cell morphology. For this reason 

 it is usually excluded from the domain of comparative em- 

 bryology of animals in the stricter sense; in this book too, it 

 will receive no consideration. Comparative embryology has 

 to do accordingly with the development of the Metazoa." ^'* 

 It is satisfactory to note that in the later general part of 

 the great text-book from which this paragraph is quoted, 

 the authors have given a much more adequate defini- 



