ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 649 



or spindle-shaped corpuscles immersed in, or held together by, a 

 colourless and more fluid plasma. In the radiating and reticulate 

 extensions from the central mass these corpuscles were sometimes 

 quiescent, but more often were seen travelling in slow and regular 

 order to and fro between the centre and the periphery ; the general 

 aspect under these conditions corresponded so nearly with the 

 characteristic granule circulation of certain Foraminifera and other 

 Ehizopoda, that it was difficult to realize that it was a unicellular 

 plant, and not a Protozoon, under examination. In the most actively 

 moving cells, almost the whole of the ovate corpuscles were deployed 

 upon, and in motion along, the radiating filaments, while in the most 

 quiescent examples both filaments and corpuscles were withdrawn into 

 the central mass. 



Motion of Diatoms.* — Mr. J. D. Cox considers that before any 

 satisfactory solution of this problem can be reached, or any decisive 

 determination whether the motion be due to osmotic or to ciliary 

 action, a good deal of patient observation must be made — both of the 

 motion itself under varying circumstances, and of the structure of the 

 diatom, including the nature of the raphe, and the question of the 

 existence of a gelatinous envelope covering free as well as stipitate 

 frustules. 



The following observations, which have recently been repeated 

 and fully verified, are copied from notes made in the summer of 

 1879, and are a contribution to the record of facts which any sound 

 theory on the subject must account for. They seem most consistent 

 with a supposition of ciliary action, though it is possible that some 

 form of osmotic action might produce similar phenomena. 



A fresh gathering of diatoms from a little brook near Cincinnati, 

 contained a number of Nitzschia linearis, which had progressed so far 

 in self-division that the front view of the frustule was twice as broad 

 as the side view, but from the peculiar form of the Nitzschia, the 

 carina was in plain view on each edge of the frustule as it lay or 

 moved on its broader side. The first case Mr. Cox noticed was that 

 of a frustule apparently held fast by the glasses of the compressor, 

 but a gelatinous mass of decomposed vegetable matter was seen moving 

 steadily along the frustules from one end to the other, making a 

 momentary halt in the middle. The mass was as large in diameter 

 as the width of the diatom, so that it reached from side to side of the 

 frustule, overlapping the carina of the valve on one side. The 

 motion of the loose matter was once or twice reversed, as if the 

 diatom was trying to back out of its position, and so produced a 

 current in the opposite direction. Presently the diatom got loose, 

 backed out and moved a considerable distance across the field, the 

 gelatinous substance still adhering and being dragged after it. Again 

 an obstruction was met, the diatom stopped, and as if the machine 

 were reversed in the new effort to back out, the foreign matter was 

 again dragged to the foremost end, and this time a smaller floating 

 particle of similar kind moved in the same manner along the opposite 



* Amer. Mon. Micr. Journ,, ii. (1881) pp. 66-9. 



