360 ANIMAL NATURE OF DIATOME^B. 



general conditions of organic beings. Having observed 

 the presence of eyes in Infusoria we forthwith proclaim 

 as eyes every red opaque spot, not merely in Infusorial 

 Animalcules but in all microscopic objects, and the pre- 

 sence of eyes is adduced as an incontestable proof of 

 their animal nature. The observations of Kiitzing, 

 already quoted, on the metamorphoses of Microglena 

 monadina into Ulothrix zonata, and of Cryptomonas 

 pulvisculus into Stigeoclonium stellare, clearly show that 

 elementary vegetables may not only manifest an appa- 

 rent movement but may also present a body similar to 

 the so-called eye in Infusoria, and the last is probably 

 nothing more than a cell-nucleus. 



Finally the division into two equal parts, or as we 

 term it the deduplication, may take place in a being 

 of complex organisation in a mode apparently similar 

 to that, by which it is effected in a simple cell. Not 

 only in the lower Infusoria, as Monades and Vibriones, 

 but in Polypi also, we see a transparent area appear first, 

 and subsequently a line of demarcation in the place 

 where a true division is effected at a later period. 



Having premised these general considerations, let us 

 examine the Diatomeae, availing ourselves of the special 

 and often cited labours of Ehrenberg and Kiitzing, as 

 well as of scattered observations by other authors, and 

 adding to these the result of our own researches. 



Every Diatomean is formed of a siliceous shield and a 

 soft substance therein contained. According to Kiitzing, 

 this shield consists of pure silica, or, in some cases, 

 perhaps, of silica combined with alumina. Nageli, further, 

 says that the silica is deposited in the outside of an 

 organic membrane, which he believes to be of a vegetable 

 nature. In fact, an organic membrane ought to exist, 

 for the silica could not become solid except by crys- 

 tallising or depositing itself on some pre-existing sub- 

 stance. On the other hand, we cannot admit, with 

 Nageli, that it has been deposited externally; for in 



