554 THE NATURAL HISTORY OF 



neighbours in the kingdom to which they themselves 

 belong, or whether even certain divisions from both natural 

 kingdoms might not properly be associated. It is only 

 with this limitation that the question, as here considered, 

 must be understood, whether Protococcus plumalis is to 

 be regarded as animal or plant ; or, since of the above- 

 mentioned genera of Infusoria some only present any 

 similarity with it, whether it is to be considered as an 

 animal belonging to the Monadina, Cryptomonadina, 

 Volvocina, or Euglence, or whether it should not be 

 referred, as an Alga, to the family of the Palmelleae. 



Although Flotow, after much consideration, comes to 

 the conclusion that Protococcus pluvialis must be regarded 

 as a plant, the reasons upon which he is induced to come 

 to this conclusion do not appear to be well chosen. They 

 are, 1. its capability of revival after having been dried 

 for months and years ; 2. the viability of separate por- 

 tions of its substance ; 3. the occurrence of gemmation 

 which, moreover, in the proper sense of the word, is more 

 than doubtful. Ah 1 of which circumstances may be 

 observed occasionally in the Animal Kingdom. 



By Morren, on the other hand, this organism, under 

 the name of Discencsa purpurea, is arranged among the 

 Infusoria in the family of the Cryptomonadina, Ehr., and 

 has assigned to it a place close to Trachelomonas volvocina, 

 Morren, (non Ehr.) Focke also conceives that the reasons 

 above assigned by Flotow for the vegetable nature of 

 Protococcm, are the rather calculated to prove its animal 

 nature. 



According to Ehreuberg, for an organism to be charac- 

 terised distinctly as an Infusorium, it is requisite that it 

 should possess a complete organisation analogous in all 

 respects to that of the higher animals ; on the other hand, 

 however, Dujardin, Siebold, Kolliker, &c., contest this, 

 considering spontaneity and contractility alone, as indis- 

 pensable criteria. 



Now to consider Protococcus pluvialis in both these 

 points of view. 



