3l8 FRANCIS DARWIN. 



which the arrangement and appearance of the vacuoles undergo 

 give us distinct evidence of internal change occurring in the 

 aggregated masses, which is quite inconsistent with the view 

 that their changes of form are impressed from without. On 

 the other hand, both the presence of vacuoles, and the fact 

 of internal changes occurring, are perfectly consistent with the 

 view that the aggregated masses are protoplasm. An observa- 

 tion of my father's points to the same conclusion. He de- 

 scribes^ how whilst one mass was rapidly increasingand another 

 in the same cell rapidly decreasing, he '' was able to detect 

 a connecting thread of extreme tenuity, which evidently 

 served as the channel of communication between the two." 



It may be worth while here to sugest a third view com- 

 bining in a certain sense my father's and the opposing theory ; 

 but it is more justly to be described as a modification of my 

 father's view. It might be possible that a condensation of 

 the colouring matter of the cell-sap should form the basis 

 of the aggregated masses, while the power of movement would 

 be supplied by particles of protoplasm separated from the 

 flowing network. In favour of this view might be adduced 

 the observations of Sachs^ on the hairs of Cucurbita, and 

 those of Kiihne^ on those of Tradescantia. Both of these 

 observers saw small portions of protoplasm separate from the 

 network under the influence of heat in one case and cold in 

 the other, and undergo amoeboid changes of form while 

 floating freely in the cell-sap. Now, if such amoeboid masses 

 were to permeate the precipitated cell-sap, spontaneously 

 moving crimson masses would be the result. 



This view must not be dismissed at once. But the fact that 

 an abundant protoplasmic current may be seen flowing, while 

 numerous aggregative masses are actively changing their 

 shape, seems to show that it is not the true explanation. 

 It must be remembered that quantity of aggregated matter is 

 very considerable ; the granular dehris produced by the death 

 of an aggregated cell almost fills the whole cavity. More- 

 over, the motive power seems to be intimately distributed 

 throughout the aggregation masses, for very minute threads 

 undergo changes of form. If, then, this motive power (in- 

 timately distributed through a large quantity of matter) is 

 supplied by the actual deduction of protoplasm from the 

 flowing network, it is difficult to see how enough of the 

 latter can be left to produce the strong currents which cer- 

 tainly coexist with active aggregation. 



1 ' Insectiv. PI.,' p. 42. 



"^ ' Physiologie Vegetale,' p. 74. 



3 'Das Protoplasma,' p. 103. 



