556 THE NATURAL HISTORY OF 



with Chlamidomonas, from which, indeed, it is scarcely to 

 be distinguished. But the latter, according to Cohn, has 

 not yet been observed in the " still" condition. 



But Pandorina and Chlamidomonas have long enjoyed 

 only a very doubtful character as animals ; Kiitzing having 

 arranged the former among the Palmellaceae, as Botryo- 

 cystis morum ; and Siebold the latter among the Algae, 

 in spite of the only certain character admitted by him as 

 distinctive of an animal nature, viz., the contractility of 

 the body. 



Protococcus plumalis, however, presents the most 

 striking analogies with genera in which this property is 

 exhibited in the highest degree, the genera Euglena and 

 Astasia, which, according to our present knowledge, 

 must be regarded as indubitable animals, their claim to 

 be so considered having even never yet been called in 

 question by any careful observer.* 



Among the points in which the closest resemblance 

 exists between Protococcus and Euglena, may be enu- 

 merated the following : 



1. The red matter in the latter presents precisely the 

 same characters, and, like that of Protococcus, is coloured 

 blue by iodine, and contains corpuscles not to be distin- 

 guished from the chlorophyll -vesicles. 



2. The colourless extremities of Euglena manifestly 

 correspond with the colourless elongation of protoplasma 

 at the two ends of the Protococcus cell ; the beak also of 

 Euglena, with its single cilium, precisely corresponds 

 with the biciliated extremity of Protococcus. 



3. The eye-spot of Euglena appears to be chemically 

 analogous with the red pigment spot in certain stages of 

 the zoospores of Protococcus ; it is equally coloured blue 

 by iodine. 



If to the above it be added that Euglena, at least 

 according to Dujardin, Siebold, and Kolliker, equally 

 presents the characters of a simple closed cell, it will be 



* This is now, by no means, the case. 



