OF THE DIATOMEJE. 53 



Gasteropoda. The primaiy cause, however, is different, and not due to any 

 property of animal vitality, but arises, in my opinion, merely from the effects 

 of vegetable circulation. I have observed several corpuscles of uniform size 

 travel to and fro apparently vrithin the membrane, which is thus raised in 

 weaves by their passage." Mr. Wenham foUows up this explanation by a 

 conjecture with respect to the rarer movements of the Desmidieae. " As 

 there are in these," he writes, " no indications of either external orifices or 

 cilia, may not their locomotion be effected by the currents of protoplasm 

 forcing their way between the primordial utricle and outer tunic, which will 

 thus be raised in progressive waves if the investment happens to be in a 

 suitably elastic condition." (See p. 5.) 



The undulating movement of an exterior membrane thus indicated by Mr. 

 Wenham, over the surface of Diatomaceous fnistules, is doubtless identical 

 -with the ciuTcnt demonstrated by Siebold by means of indigo (J. M. S. 

 i. pp. 196, 197). The latter states that the particles of this colouring matter 

 which come in contact with the living NavicuJce are set into a quivering 

 motion, although previously quite motionless ; but this happens only along 

 the lines of the foiu" sutures, the particles adherent to other parts of the shield 

 remaining motionless. " The indigo particles, which are propelled from the 

 terminal towards the two central eminences, are never observed to pass 

 beyond the latter : at this point there is always a quiet space, fi'om which 

 the particles of indigo are again repelled in an inverse direction towards the 

 extremities. This proves that the linear sutures, as may in fact be seen, 

 do not extend over the central eminences of the shield. The current at these 

 clefts is occasionally so strong, that proportionally large bodies are set in 

 motion by it." The sutures and clefts alluded to by Siebold, it should be 

 imderstood, are not the sutures between the valves and connecting membrane, 

 but the evident lines extending between the apparent pores on the valves, 

 and w^hich, to his apprehension, are actual fissm^es in the silicious envelope, 

 by which " the delicate primordial membrane which lines the sihcious shield 

 can be brought into close relation with the external world." This belief in 

 the presence of such fissm^es on the valves we have previously examined and 

 shown to be unfounded. (See p. 41.) 



Prof. Smith has the following remarks on this debateable point of the 

 cause of the motions of Diatomeae {op. cit. vol. i. p. xxiii) : — " Of the cause 

 of these movements, I fear I can give but a very imperfect account. It 

 appears certain that they do not arise from any external organs of motion. 

 The more accui'ate instruments now in the hands of the observer have enabled 

 him confidently to affirm that all statements resting upon the revelations of 

 more imperfect object-glasses, which have assigned motile cilia, or feet, to 

 the Diatomaceous fi'ustule, have been founded upon illusion and mistake. 

 Among the hundreds of species which I have examined in every stage of 

 growth and phase of movement, aided by glasses which have never been 

 surpassed for clearness and definition, I have never been able to detect any 

 semblance of a motile organ ; nor have I, by colouring the fluid with 

 carmine or indigo, been able to detect, in the coloured particles surrounding 

 the Diatom, those rotatory movements which indicate, in the various species 

 of true infusorial animalcules, the presence of cilia. I am constrained to 

 believe that the movements of the Diatomaceae are owing to forces operating 

 within the frustule, and are probably connected with the endosmotic and 

 exosmotic action of the cell. The fluids which are concerned in these 

 actions must enter and be emitted through the minute foramina at the 

 extremities of the silicious valves ; and it may easily be conceived that an 

 exceedingly small quantity of water expelled through these minute aper- 



