ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 109 



several times, is thoroughly convincing, and establishes with perfect 

 certainty that the cause of the motile phenomenon is the peculiar 

 distribution of the osmose in the cell. 



I have thus described all the facts observed by me, which, as I 

 think, must secure for the osmotic hypothesis the decided preference 

 over the protoplasmic. 



Taking the above observations as a basis, we may account for the 

 process which takes place in a moving diatom as follows : — In a 

 quiescent cell the phenomena of exosmose and endosmose occur with 

 equal intensity and simultaneously over the whole surface. Before 

 the movement begins the exosmose becomes more intense at one end 

 of the cell than at other parts of it, doubless by reason of the altered 

 density of the cell-contents there, which might happen from alimentary 

 and other physico-chemical processes. This increase of intensity 

 continuing for some time the result at length is that the exosmose 

 (analogous to the effluent water in Segner's water-wheel) sets the 

 diatoms in motion. 



The vibration of the micrococci leads necessarily to the conclusion 

 that the exosmose, which, while the cell is at rest, is distributed like 

 the endosmose uniformly over the whole surface, is, on the contrary, 

 concentrated, when it moves, exclusively at one end of the cell : the 

 distribution of the endosmose remains however unchanged. The 

 intensity of the two phenomena, i. e. the quantity of water passing 

 in and out, must be equal to each other ; since however the expulsion 

 of the water is concentrated at one end only of the cell, and there- 

 fore a small portion of its surface, the action of exosmose naturally 

 displays greater force and extends further. At the rest of the cell 

 surface, where a comparatively feebler and slower endosmose takes 

 place, the motion is less intense and extends to a shorter distance. 



If, after all we have said, some are not quite satisfied that the 

 external protoplasmic layer is not the cause of motion, and that the 

 osmotic process is, every one, I think, must be convinced that osmose 

 is one of the causes on which the motion depends." 



Grammatophora longissima, Petit.* — Under this name P. Petit 

 described a beautiful diatom from Campbell Island and New Zealand, 

 distinguished by its very long and narrow frustules and by the large 

 number of the undulations of the septa. F. Castracane has now 

 found in Italian waters what appears to be the same species, which he 

 thus describes : — • 



Grammatophora longissima Pet. var. italiea. Gr. elongata, sexto- 

 septuplo longior quam lata ; dissepimentis 6-7 undulatis, et ad apicem 

 capitatis ; valvis curvatis, striis subtilissimis 2900 in millimetro, Frus- 

 tula usque adhuc inventa in seriem lateralem conjuncta. Longitude 

 = mm. 0-0585 ; latitudo = mm. 0-00835-0-00975. Habitat in mari 

 Adriatico et in Tyrreno. 



* Atti Soc. Crittogam. Ital., xxiv. (1881) pp. 25-32. 



