12 GENERAL CONSIDERATIONS 



which he was followed by a majority of the "nature-philosophers," most 

 of whom gave little or no attention to the Protozoa, but, accepting Miil- 

 lers' work as final, based many of their speculations upon it. 



It is rather remarkable that fifty years or so later, when the biological 

 atmosphere was saturated with the idea of the cell theory, the justly 

 famous microscopist of Europe, C. G. Ehrenberg (1795-1876), using 

 much finer achromatic lenses, should have returned to the crude view 

 of Leeuwenhoek, assigning to the Protozoa a system of minute but com- 

 plete organs. His conclusions on Protozoa were brought together in one 

 great work, the title of which alone shows his point of view [Die 

 Infusionsthierchen ah vollkoinmene Organhmen, 1838). From the sup- 

 posed possession of many stomachs he gave to one of his groups the 

 name Polygastrica or Magenthiere, making it a sharply defined class 

 of the animal kingdom. One of the sub-classes in which these supposed 

 stomachs were apparent he called the Enterodela, while all other forms he 

 included as Anentera. The red pigment spots of many forms were inter- 

 preted as true eyes, but as eyes could not be conceived without an ac- 

 companying nervous system, he sought for nerve ganglia in different 

 organisms and found what he was looking for in a species of Astasia. 

 He described the "eye" in this form as seated upon a "spherical granular 

 mass" which he considered as equivalent to the suprapharyngeal ganglion 

 of the rotifers. The myonemes in the stalks of Vorticella, in Stentor, and 

 in many other ciliates he interpreted as muscles. Pigment spheres and 

 protoplasmic granules were described as ovaries, the nucleus as a testis, 

 while the contractile vacuole was at first regarded as a respiratory organ 

 (see Weatherby, infra, Chapter VII), 



A formidable opponent of Ehrenberg soon appeared in France — Felix 

 Dujardin, who, influenced by long study of the Foraminifera, came to 

 the conclusion in 1835 that these rhizopods, which up to that time had 

 been classified with the cephalopod molluscs, were in reality the simplest 

 of animal organisms, composed of a simple homogeneous substance to 

 which he gave the name Sarcode. 



Dujardin is best known by his systematic treatise on the Protozoa which 

 he published in 1841, and in which he laid the basis for the modern 

 classification of these unicellular forms. The first suggestion that Proto- 

 zoa might be single cells was made by Meyen ( 1839) , who compared the 

 infusorian body with a single plant cell. But, according to Biitschli 



