366 ALFRED GIBBS BOUENE. 



by the addition of a 1 to £ per cent, solution of common salt, 

 the protoplasm shrinks, owing to withdrawal of imbibition 

 water. This might, of course, take place through the pellicle, 

 but this is not probable, as such a layer must be impermeable, 

 or difficultly permeable, to water, if it have the function of 

 protecting the central protoplasm from the action of water; 

 and, in any case, when a sudden shrinking took place, one 

 might expect to see some crenatiou of the surface, such as 

 is exhibited by a human red corpuscle when it is exposed to a 

 medium denser than its own plasma. No such crenation 

 takes place ; but, on the other hand, some portions of the 

 protoplasm usually stick to the cover-glass and become torn 

 off, while some of the protoplasmic contents escape into the 

 water and are carried away by the current. 



I have at times observed a similar phenomenon when a long 

 pseudopodium was quickly withdrawn. A specimen of P. 

 viridis, which has been moving about under a cover-glass, 

 habitually leaves some portions of itself sticking to the glass. 

 Appearances, such as are shown in fig. 2, constantly occur 

 where a pseudopodium is retreating, and are due to the stick- 

 ing of the superficial protoplasm to the glass. 



I have also constantly seen villi, such as Gruber^ has 

 figured for P. villosa, formed in the same manner. 



Such phenomena seem to me to render the existence of 

 any pellicle unlikely. Moreover, as will be described below, 

 when a specimen of P. viridis is torn into pieces with 

 needles the water seems to penetrate and cause almost instant 

 disintegration. Now, if the protoplasm of these forms is in 

 the habit of forming a pellicle directly any new surface is 

 exposed to the water, why does it not do so in this case ? It 

 appears more probable that so long as the protoplasm is alive 

 the amount of imbibition water which can be taken in is 

 regulated, and that in the instance above cited the protoplasm 

 is killed by a shock caused by the teasing, so that excess of 

 water can at once penetrate and cause disintegration. 



The pscudopodia are usually very blunt and lobose, and 

 ' ' Zeit. f. w. Zool.,' Bd. xli, pi. xiii, fig. 3. 



