12 THE USES AND ORIGIN 



the elements. They require not to seek their food, since 

 the inorganic materials and simple compounds sufficing 

 for their nutrition habitually exist around and in contact 

 with them. 



On the other hand, in animal organisms next above the 

 Amoeba — such as the various forms of Ciliated Infusoria 

 and Rotifers — well-marked powers of locomotion are dis- 

 played, and we have to do with creatures which, if they 

 do not ' seek,' at all events seize and swallow solid food. 

 We find in the latter of these forms of pond life, distinct 

 channels through which food is taken in and absorbed ; 

 we have glandular structures of various kinds ; we have 

 organs of locomotion, internal and external. Thus, though 

 we have not yet been able to detect with any certainty 

 even the rudiments of a nervous system, the grade of 

 vitality of these animal organisms must be at once ad- 

 mitted to be notably higher than that of plants. The 

 degree of correspondence existing between such creatures 

 and their surroundings is already much more varied 

 than that existing between vegetal organisms and their 

 medium ; and this kind of complexity of relation steadily 

 increases in animal organisms only a little higher than 

 those to which we have already referred. Their responses, 

 moreover, to the varied external influences to which they 

 have become amenable are effected by movements direct, 

 rapid, and comparatively complex — the motions them- 

 Belves being brought about by muscular contractions, partly 

 simultaneous and partly successive, and mostly occurring 

 in groups which are definitely related to difierent external 

 impressions. Reference to a few of their common muscular 

 actions will illustrate this. 



Conjoined movements of the head and its appendages 

 are needed for the seizure of fragments serving as food ; 

 and these motions must be followed by certain others in 



