PROTOCOCCUS PLUVIALIS. 555 



First, as regards Ehrenberg's doctrine. The organisa- 

 tion of Protococcus may very plausibly be referred to that 

 of the anenterate Infusoria, as understood by that ob- 

 server ; in this case the enveloping cell might perhaps be 

 explained as the shield ; the primordial cell as the proper 

 body of the animal ; the chlorophyll- vesicles, colourless 

 granules, and cytoblasts, as the testes ; the red and green 

 globules as ova; the frequently existing red pigment spots 

 as eyes ; the vibratile cilia as a proboscis ; the hyaline 

 spot as mouth ; and the vacuoles as stomachs. At all 

 events the organs which Ehrenberg has figured and 

 described as of such nature in Trachelomonas, Fblvox;, 

 Euglena, Chlamidomonas, Closterium, Euastrum, &c., 

 present such appearances that, although they are in reality 

 organised in an essentially different way, they cannot be 

 optically distinguished from what they are represented 

 to be. 



On the other side, these bodies correspond in all 

 respects with the organisms which are found either 

 absolutely in indubitable plants, or in the spores of such 

 plants. 



Whence it is apparent that the proof of an animal 

 organisation offered by Ehrenberg, does not suffice in 

 doubtful cases incontestably to prove the animal nature 

 of a doubtful creature when alive, because formations are 

 presented even in plants which cannot be directly shown 

 to be distinct by optical or chemical means, but only 

 indirectly, with the aid of analogy. 



If, on the contrary, that view of the structure of the 

 Infusoria be the more correct, which regards them only 

 as simple contractile cells, and all the above elementary 

 parts as parallel, not with animal but with vegetable 

 organisms, we arrive at more comprehensive conclusions. 



One of the characteristics of Protococcus is this, that it 

 affords analogies, at different periods of its growth, not 

 with one only, but with many genera hitherto considered 

 distinct. Thus the motile, or " swarming," form agrees 

 with the genus Pandorina, Ehr., or more closely still 



