106 SUMMARY OF CURRENT RESEARCHES RELATING TO 



theory as being less well founded and probable than tbe first. If we 

 also take into consideration that the osmotic theory does not require 

 the assumption of any external protoplasm which no one has yet seen, 

 it has a certain advantage over the other. 



The author then proceeds to describe the direct observations made 

 by him which he considers prove that osmotic phenomena are the 

 cause of the movements of the DiatomaceaB.* 



" In January 1879, being mainly occupied in zoological investiga- 

 tions at the zoological station of Nai)les, I had an opportunity of 

 observing three species of Diatomacefe, which are very common in the 

 sea there. They were two species of Navicula (one a very large 

 kind) and a Stauridium. A vessel of sea-water containing algfe from 

 the shore, after standing for some days and acquiring an offensive 

 smell, showed a number of the smallest micrococci, amongst which, in 

 a drop taken from the bottom, a considerable number of the above 

 Diatomacefe were swimming. 



With regard to their motion the following particulars were 

 observed : — 



(1) The usual motion backwards and forwards, with intervals 

 of rest. The algse always lay not horizontal but obliquely, so 

 that one end touched the slide whilst the other was somewhat raised. 



(2) Besides a rectilinear motion, a lateral rotation of the whole 

 alga was observed, the raised end describing a circle whilst the other, 

 which adhered to the slide, occupied the centre. 



Pursuing my observations further in this direction, I noticed the 

 following attendant phenomena : — 



(1) First a violent vibration of the micrococci in the immediate 

 neighbourhood of the living diatom, whilst the others, lying farther 

 from it, or near to the dead ones, or to other foreign substances — 

 sand-grains, &c. — displayed no such violent movements.f 



The vibration was most violent in the micrococci nearest to the 

 diatoms. They threw themselves from one side to the other in a very 

 regular fashion. The more distant the micrococci were from the 

 algas the slower their movement was, and finally it ceased altogether 

 at a certain distance (about half the length of the diatom). In this 

 way a living diatom appeared to be surrounded by a perfect sphere of 

 micrococci, vibrating more or less. 



This phenomenon justifies the conclusion, not only of the existence 

 of osmotic forces, but also that they possess considerable intensity. 



* [The author makes no mention of English observers, but it may be pointed 

 out that the suggestion that the movements of diatoms are caused by exosmose 

 and endosmose, was made by \V. Smith in 1853. Cf. ' Synopsis of the Diato- 

 maceae,' i. (1853) Introduction, pp. xxii.-iv. See also the objections of the 

 editors of the ' Micrographic Dictionary,' 3rd ed. (1875) p. 237; Dr. Carpenter's 

 reply in ' The Microscope and its Revelations,' oth ed. (1875) pp. 318-19. The 

 object of M. Mereschkowsky's paper is to give a direct proof of the fact. — Ed. 

 J. R. M. S.] 



t Although I do not now remember the fact, and find no mention made of it 

 in my notes, yet I think that probably all the micrococci were displaying the 

 so-called molecular or Brownian movement. At all events this latter, on account 

 of its feebleness compared with the strong and violent vibration of the micrococci 

 under the circumstances described above, wbuld be unimportant. 



