260 CASTRACANE, ON DIATOMACEyK. 



gradually became slower, and at last scarcely apparent. Some 

 minute floating corpuscles in proximity to 'these active cysts 

 ■were suddenly attracted, as it were, into a vortex whence 

 I concluded that the movement of the two cysts in 

 question was due to vibratile cilia. In fact, I discovered 

 two excessively delicate cilia in both of the cysts, dis- 

 posed in opposite directions, in the most lively motion, 

 and longer than the diameter of the cyst, which, from 

 the presence of these appendages, was proved to be a true 

 zoospore. 



I have since omitted no opportunity of making further 

 observations respecting the circumstances accompanying the 

 production of the Diatomacea, being persuaded that, from an 

 exact knowledge of these conditions, we may probably be 

 able to deduce laws serving to fix the limits of the species at 

 present so uncertain, by distinguishing in the various forms 

 of the diatoms the true diagnostic characters from the varia- 

 tions, affording either temporary indications of the age of the 

 individual or abnormally arising from a monstrous produc- 

 tion determined by accidental circumstances, amongst which 

 may be enumerated the place of birth and the development of 

 the diatom. Among the different observations 1 have made, 

 and the peculiarities I have noticed, 1 would relate that, having 

 placed another of the little green masses, taken from the same 

 aquarium, in an apparatus in which an object could be re- 

 tained in water for many days without being disturbed, after 

 some time the glass with which the preparation was covered 

 began to exhibit a considerable extent of surface sprinkled 

 over with extremely minute green corpuscles. Some of these 

 appeared as round points, whilst others were slightly oval, 

 amongst which the smallest appeared to be composed of a 

 green substance, whilst others, of larger size and more deve- 

 loped, presented the aspect of an oval cell enclosing two 

 distinct masses, and the largest exhibited no difference from 

 a very small Navicula.- 



These observations respecting the reproduction of diatoms 

 from isolated germs is in no way opposed to the endogenous 

 mode above referred to, according to which they are organized 

 within a cyst, since the different mode of reproduction might 

 indicate specific differences, and in any case the occurrence 

 of such apparent anomalies in the reproduction of the lowest 

 members of the vegetable kingdom is familiar to any one 

 engaged in their study. 



A more constant character, that I have observed on every 

 occasion in which I have noticed diatoms in the nascent or 

 young condition, is the peculiar colour of the endochrome. 



