

2 AMEBOID MOVEMENT 



of movement, feeding habits and gross structure. The great im- 

 portance of the functions that have been ascribed to leukocytes, 

 and their very widespread occurrence in the higher animals has 

 served to give rise to the belief that ameboid characteristics were 

 not unique among animals, but common to many of them. The 

 discovery of ameboid movements among plant zoospores, among 

 animal ova, in the endoderm cells lining the digestive tract of a 

 great variety of animals, in the nuclei of some animal cells, in 

 the wandering cells of sponges and other animals all these in- 

 stances of ameboid movement occurring in such widely different 

 tissues inevitably placed it among the most important phenomena 

 known to occur in organisms. 



Out of the discovery that ameboid movement may be exhibited 

 in some form or other in so many different kinds of organisms, 

 grew the theory that even muscular movement as known in man 

 and the higher animals is at bottom a specialized sort of ameboid 

 movement; not merely phylogenetically, but as it is now known. 

 As we shall see however in the following pages, this theory of 

 muscular movement cannot be based specifically on the streaming 

 process per se, but it is very probable, on the other hand, that the 

 same process which underlies contraction of the ectoplasm in the 

 ameba also underlies contraction in muscular tissue. 



But this remarkable story of the development of a single unre- 

 lated observation into a widespread biological phenomenon is not 

 yet complete. With its further development the following pages 

 are concerned. It will be shown that the movement of the sur- 

 face film of the ameba is analogous to that of some blue-green 

 algae, diatoms and crawling euglenas, in which organisms the sur- 

 face film seems to be the vehicle of movement. Thus the ameba 

 finds itself related to these organisms by new ties. More im- 

 portant still is the significance of the wavy path of the ameba, 

 which may possibly be due to the same fundamental mechanism 

 that controls, under suitable conditions, the direction of the path 

 in man and many other animals and motile plant cells. Thus the 

 phenomenon of ameboid movement born in nakedness and utter 

 isolation, has become attired, in a brief space, with the Victorian 

 garb of a Fundamental. 



