i8 



CHAPTER n. 



AMCEBA. 



IT has been wisely said that " the highest laws of our 

 science are expressed in the simplest terms in the 

 lives of the lowest orders of creation " (Paget) ; and 

 it will be well, therefore, to commence our studies 

 with a close investigation into the characters of one of 

 the simplest of living animals. 



The word Amoeba is a generic term,* which is 

 applied to a number of forms, which have in common 

 the following characters ; they are more or less 

 minute specks of nucleated protoplasm, without any 

 wall or membrane limiting their surface, and they are 

 capable of pushing out processes of their body sub- 

 stance from any part or point of it. They are some- 

 times as much as one-hundredth of an inch in 

 diameter, but they in. all cases require the assistance 

 of a microscope of high powers for their satisfactory 

 study. 



If we place one on. a glass slide, and, after allowing 

 it to become used to its new position, examine it 

 under the microscope, we shall at once see how ap- 

 propriate is the name that has been given it. Its 

 form is never constant for more than a few moments 

 together, as we can best demonstrate! by making a 

 sketch of its shape once every minute for some five or 

 six times. 



These changes in form are, we know, expressions 

 of the irritability and contractility of the protoplasm. 



* The possibility that a number of so-called Amoebae are 

 stages in the life-history of animals or plants does not affect the 

 question here dealt with. 



