356 PROGRESS OF SCIENCE IN THE CENTURY. 



that of a simple vesicle, from which every animal is 

 evolved, not only theoretically, but historically." * 

 Considering the date we cannot regard the statement 

 as other than a marvellous premonition. 



In 1835, Robert Brown showed that a nucleus was 

 normally present in all vegetable cells, thus raising 

 Fontana's discovery to a higher level of importance. 

 And, in the same year, Johannes Miiller made a 

 definite comparison between the cells of plants and 

 those of the notochord in animals, — ^the beginning of 

 a recognition of the fundamental unity of vegetable 

 and animal structure. The observations of Dujar- 

 din, Purkinje, Von Mohl, Valentin, linger, ISTageli, 

 Hofmeister, Henle, and many others might also be 

 alluded to. 



This is no complete history, but we have cited 

 enough to show how very gradually the way was 

 prepared for the formulation of the cell-doctrine 

 by Schwann and Schlieden in 1838-39 f " The 

 " significance of Schleiden's, and especially of 

 " Schwann's, work lies in the thorough and compre- 

 " hensive way in which the problem was studied, 

 " the philosophic breadth ^vith which the conclusions 

 " were developed, and the far-reaching influence 

 " which they exercised upon subsequent research." 

 In this respect it is hardly too much to compare the 

 MihrosJcopiscJie Untersuchungen with the Origin of 

 Species. 



* Cited from Dr. Hans Gadow's notes to Haeckel's Last Link, 

 1898. 



t Sir William Turner, " The Cell Theory, Past and 

 Present," Inaug. Address Scottish Microsc. Soc, 1890, and 

 in Nature, 1890 ; Prof. J. G. McKendrick, " On the Modern 

 Cell Theory " (Proc. Phil. Soc, Glasgow, 1888), and in his 

 text-book of Physiology ; P. Geddes, articles Morphology and 

 Protoplasm, Encyclopcedia Britannica, 



