INTRODUCTION g 



Unlike his predecessors, Miiller did not regard the Protozoa as 

 complicated animals, but considered them as the simplest of all living 

 things, composed of a homogeneous gelatinous substance, a view in 

 which he was followed by a majority of the " Nature-philosophers " 

 (Lamarck, Schweigger, Treviranus, Oken), most of whom gave little 

 or no study to the Protozoa, but, accepting M tiller's work as final, 

 based many of their speculations upon it. 



It is difficult to understand why, after M tiller's work, the next great 

 authority, C. G. Ehrenberg (i 795-1 876), the renowned Berlin micro- 

 scopist, using much finer achromatic lenses, should have returned to 

 the crude view of Leeuwenhoek, assigning to the Protozoa a system of 

 minute but complete organs. His conclusions on Protozoa were 

 brought together in one great work, the title of which alone shows his 

 point of view : " The Infusoria as Complete Organisms " (Die Infu- 

 sionstliierchcn als vollkommene Organismcii). He was primarily a 

 student of their finer structure, and the details of organization, although 

 erroneously interpreted, were clearly described. In working out the 

 internal structures he made use of Gleichen's experiments in feeding. 

 The animals were seen to ingest the powdered carmine, so that the 

 boundaries of the internal gastric vacuoles were clearly marked. He 

 followed these particles as they passed from the mouth into the oesoph- 

 agus and thence into one of the many digestive or gastric vacuoles 

 found in the inner plasm of nearly all Protozoa. He saw that the 

 particles followed clearly defined paths which might be straight or 

 curvilinear, or otherwise varied in different forms, but which always 

 ended in a more or less clearly marked anal opening. He saw also that 

 the parts of the supposed tract nearest the mouth fill first; that they 

 become globular, and that successive reservoirs become filled, down to 

 the posterior end of the body. He inferred from this the existence 

 of a digestive tract, concluding that the parts thus filled were stomachs. 

 As soon as the first was filled, the overflow of food passed on into 

 another stomach. From the supposed possession of many stomachs 

 Ehrenberg gave to this group the name Polygastrica or Magentliicre, 

 making it a sharply defined class in the animal kingdom. To all 

 forms in which he could find no stomachs, but in which he supposed 

 that mouth and anus were the same opening, he gave the name of 

 Anentcra (gutless), while to forms with many stomachs he gave the 

 name Enterodcla (gut-bearing). 



The red pigment spots of many forms were interpreted as true eyes, 

 but as eyes could not be conceived without an accompanying nervous 

 system, he sought for nerve-ganglia in different organisms, and 

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

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

 glandular mass," which he considered equivalent to the supra-pharyn- 



