CASTRACANE^ ON DIATOMACE^. 259 



radians, and by Smith in November of 1853 in the same 

 species ; and I had myself an opportunity of making the 

 same observation in the spring of 1856 in a gathering of 

 Cocconeis placentula made near Palazzuolo, under the aque- 

 duct of the Fountain of Albano. 



But it appears to me impossible longer to entertain any 

 doubt as to the reproduction of the Diatomacese by germs 

 after the observations which I have been able to make during 

 the months of February and March last (1868). With the 

 view of studying the development of these organisms I com- 

 menced by exposing to the light a- cup of water of Trevi, in 

 which on the 10th of February I had immersed a small piece 

 of a green pellicle, which was picked by the point of a lancet 

 from a small mass of refuse. This little aquarium, covered 

 with a piece of glass and exposed in the window, at the end 

 of a few days presented a beautiful vegetation of minute 

 green masses, many of which rested on the bottom of the 

 aquarium, whilst others coated its sides, and some were seen 

 floating on the surface. On the 26th of February one of the 

 minute floating masses was subjected to microscopic observa- 

 tion under a thin glass cover. It exhibited an innumerable 

 multitude of beautiful green spherical spores, inclosed in a 

 granular substance, in which might be perceived some nuclei 

 or rounded corj)uscles of a bluish or glaucous green colour. 

 All the spores did not present the apparently uniformly 

 granular contents, many exhibiting, together with a gradual 

 disappearance of the granular aspect, some in more and some 

 in less degree, a disposition to become organized into various 

 distinct masses, with such gradations as to show the identity 

 of nature between the granvilar spores and the very numerous 

 hyaline cysts which were visible in the same mass. These 

 cysts included two, three, or more navicular forms, furnished 

 with a glaucous green endochrome and with two large vesicles, 

 probably oily from their strongly refractive aspect. It was 

 imjDOSsible to entertain any doubt as to these bodies being 

 diatoms, for, having slightly moved the covering-glass, some 

 of the cysts were ruptured, and allowed the escape of the 

 navicular corpuscles, which, as they were carried away by 

 the cvuTent, exhibited alternately the elliptical side and 

 rectangular /row^ of the frustules. Besides this some valves 

 were noticed deprived of their endochrome, which, when 

 attentively examined, plainly showed the usual median line 

 and central nodule. 



Amongst the numerous hyaline cysts in a state of quies- 

 cence enclosing diatoms I noticed two Avhich exhibited a 

 gyrating motion, which was at first extremely active, and 



