OF HETEROGENESIS 225 



power in Fig. 36, A, going through their usual changes ' ; though 

 one or more cells in many of the groups were found to present 

 none of these organisms, and to be crowded with specimens of 

 Actinophrys only. All the sub-terminal, and other larger cells, 

 were found to be in a similar condition and crammed with 

 Actinophrys ; the only other organisms met with in these cells 

 being dense masses of motionless Bacteria — an association which I 

 find to be invariable in this kind of change. It is one which does 

 not take place simultaneously throughout the whole length of the 

 cells, but extends steadily from one end of the cell to the other. 

 Roughly speaking the order is this : the Bacteria multiply more or 

 less notably, while the green chlorophyll corpuscles disappear, and 

 are replaced by specimens of Actinophrys. 



Where this change is advancing through a cell, careful exami- 

 nation will always show a mixed zone intervening between the 

 healthy and the changed regions of the cell — that is, between its 

 green and its drab areas. In the latter region nothing but a dense 

 mass of Actinophrys, mixed with Bacteria and starch granules, is to 

 be seen — some of the specimens of Actinophrys being completely 

 decolourised, while others show a few green, mixed with colourless, 

 granules in their interior. Next to this area of complete change 

 we have an intermediate zone, in which small specimens of 

 Actinophrys and chlorophyll corpuscles are intimately intermixed ; 

 while beyond it we have green chlorophyll corpuscles only — all of 

 them more or less loaded with starch granules or scales. This 

 particular change being most prone to occur in old specimens of 

 Nitella which have been kept for some time in the house and then 

 treated as I have described, it will commonly be found that the 

 chlorophyll corpuscles are, in such specimens, crowded with starch 

 granules and are, as a consequence, very greatly enlarged. 



A more thorough and searching examination of the intermediate 

 zone will show that all the smallest specimens of Actinophrys are 

 of just the same size as the chlorophyll corpuscles — that none 

 are to be found smaller than these corpuscles ; that they have, at first, 

 no rays ; that they are motionless ; and that not one of them can 

 ever be seen to divide. 



What then is the mode of origin of all these myriads of 

 Actinophrys which, within a few days, will appear within the 

 closed cells of the Nitella ? Do they come from without ? This 



' These changes have been very fully described in my " Studies in Hetero- 

 genesis," pp. 245-266. 



15 



