380 



GENERAL PHYSIOLOGY 



layer. If in this stage the radiolarian be given a strong shock, it 

 may be seen that the liquid mass of slime increases and becomes 

 at the same time thicker and firmer ; this is manifested more dis- 

 tinctly when the shock is repeated.^ The mechanical stimulation 

 promotes visibly the secretion of slime. 



No excitation-effects of mechanical stimulation upon the pheno- 

 mena of form-changes, upon growth and cell-division, are thus far 

 known. 



Effects of excitation upon the phenomena of the transforma- 

 tion of energy have been investigated very fully, and a great 



.*fe 



1''1G. 171, — ThaUusicolla nucUata, a spherical radiolarian cell. A, Uninjured individual in optical 

 section. In the middle lies the central capsule, containing: the nucleus, surrounded by black 

 pigment. B, Central capsule removed. It has ah-eady surrounded itself with a new circlet 

 of pseudopodia. C, The same central capsule after strong stimulation. The pseudopodia are 

 somewhat drawn in, and between them a thick mass of slime has been secreted. B and C 

 strongly magnified. 



mass of observed facts exists. From these we will select the 

 typical phenomena. 



Those connected with motion, which are called out bj' mechanical 

 stimuli, constitute here also the chief point of interest. The pro- 

 duction of turgescence-movements in the so-called sensitive plants, 

 such as the delicate Mimosa pudica, is generally known. Mimosa, 

 which resembles a small Acacia tree, during the day and while 



1 Cf. Verwora('91). 



