332 Report S.A.A. Advancement of Science. 



a hollow protuberance of the cell wall; this is met by a correspond- 

 ing protuberance from the female cell, and the two projections unite 

 to form an oj^en canal through which the protoplasm of the male 

 cell migrates to the female cell. It sometimes happens, however, 

 owing to inequality in the sizes of the cells, that there may be a cell 

 in one filament which lies between two cells of the other filament, 

 and which can find no mate. In this case the solitarv- cell remains 

 quiescent, and exhibits few or none of those remarkable activities 

 which characterise the conjugating cells on either side of it.* 



Here it is obvious that in the case of two cells lying opposite 

 to one another, though not in contact, and though each is enclosed 

 in a firm cell-wall, some stimulus is transmitted from one to the 

 other which calls forth a definite response in the formation of the 

 connecting canals and subsequent phenomena. It might perhaps 

 be (and, indeed, actually has been) argued that the stimulating effect 

 is due to the secretion of some chemical substance by the cells in 

 question, as has been shewn tO' be the case in the attraction c f the 

 ■spermatozoids toi the archegonia of ferns, but this chemiotactic 

 explanation appears tO' be quite insufficient in view of the 

 important fact that cells which have no mate do not form gametes 

 and may undergoi no' change, though also apparently exposed to the 

 influence of any chemical substances in the surrounding water. 



If, then, one cell can stimulate another at a distance without 

 any material connection whatever, it would seem that there is no 

 great improbability involved in supposing that every cell of the 

 animal or vegetable body, at least in its earlier stages of development, 

 before it has become too specialised, may be more or less influenced 

 by every other cell in the body which is not too much specialised, 

 as well as directly or indirectly by the external environment. Any 

 modification of one part of the body, involving a disturbance of the 

 internal equilibrium, may naturally be expected to produce some 

 corresponding modification in the germ-cells, and perhaps also in 

 other parts of the body itself, and this may be the clue to the explana- 

 tion of correlated variations. 



When, of course, as in the higher animals, an elaborate nervous 

 system is developed, the influence of one part of the body upon 

 another is greatly facilitated — we have, to use our physical analogy, 

 a system of telegraphy with wires supplementing, and perhaps to 

 some extent supplanting, a system of telegraphv without. But in 

 the lower organisms, and in the early stages of development of all 

 organisms, there is no nervous system, and in such cases we must 

 suppose that the internal equilibrium is maintained either by forces 

 acting at a distance without material connections or through the 

 medium of undifferentiated protoplasm. 



* I say, " lew or none," because it occasionally happens that two cells may 

 compete with one another for a mate ; but, as far as my own observations go, 

 only one is successful, and the other never gets even as far as the breaking up of 

 the spiral chromatophore preparations to the formation of the gamete, though a 

 more or less developed protuberance of the cell-wall may be formed, and may 

 •even be met by a corresponding protuberance from the opposite cell-wall. 



