450 E inter on Growth and Inheritance 



ments of very lowly organisms, which might, at first sight, 

 be mistaken for voluntary movements. Thus, Myxcmiycetes, 

 which, at one stage of its existence, seems to wander as an 

 almost fluid mass of protoplasm, is an example of such lowly 

 organisms. He tells us how its gradual, creeping motion is 

 determined by the progressive drying up of the substance on 

 which it rests, which causes it to be attracted to adjacent 

 parts, which retain their moisture longer. Unequal distri- 

 butions of warmth, or of oxygen, have similar effects. If 

 its fluid substance, or ' plasmodium,' is brought in contact, 

 on one side, with solutions of common salt, saltpetre, or 

 carbonate of potash, it will withdraw from such dangerous 

 vicinity, while infusions of tan, or dilute solutions of sugar, 

 will attract it. It will also withdraw itself from light, and 

 it has a truly wonderful faculty of avoiding harmful matter, 

 traversing its supporting substance in aU directions and 

 taking up such materials as it may require. 



But besides giving evidence in favour of the essential dis- 

 tinctness of sensitive from non-sensitive organisms. Professor 

 Eimer makes some valuable remarks in opposition to the 

 view that unicellular and multicellular organisms are so dis- 

 tinct as they have, we beheve too hastily, been assumed to 

 be. This distinctness is generally assumed to be so great 

 that no structure formed from cells in the latter group can 

 be reaUy equivalent to any differentiation which can arise 

 within a single cell. Those minute infusorians known as 

 vorticellse are each supported on a long stalk which, upon 

 a very light stimulus, w^ll suddenly coil upon itself, and 

 so bring the vorticella attached to it near to the point 

 where the stalk is itself attached. Now the vorticeUa, 

 with its stalk, together consist but of one single cell. In 

 all multicellular animals, organs of motion or muscles are 

 formed from cells, and are equivalent to a greater or less 

 number of such. It would seem, therefore,^ that a whole 



1 See ante, p. 399. 



