THE LOWER FOEMS OF LIFE. 21 



flinty remains form some of the most exquisitely beautiful objects 

 under the microscope, and of which I believe nearly two thousand 

 species have already been described by Dr. Greville and others are 

 not allowed to be claimed by the botanists unchallenged. I remember 

 the late Dr. Trail, of Edinburgh a man of very great information 

 came to the conclusion that they were of an animal nature, because 

 in Norway there is known an earth called the "bread earth," which 

 in times of scarcity is eaten by the poor as a substitute for bread, 

 and which, when examined by the microscope, is found to contain 

 vast numbers of Diatoms. 



Now it will be admitted there will be less force in Dr. Trail's 

 inference, when it is considered that plants alone have the power of 

 forming the material of animal structure viz., proteine. This the 

 animal cannot form itself, and it becomes one of the cardinal 

 distinctions between the two great kingdoms of nature. 



If, however, I am asked to give any distinct rules by which the 

 microscopical student may at once distinguish the protophyton from 

 the protozoon, I cannot do so. Our knowledge upon this point is 

 entirely based on the dicta of the authorities in science, to which, 

 however, as a rule, we may very safely defer. 



Taking, therefore, the highest authorities as my guide, I shall now 

 draw your attention to an examination of the lowest known form of 

 animal life. 



In the intestines of insects, worms, and mollusks, the microscope 

 will detect small cellular bodies moving about by means of undula- 

 tions of their cell walls. These are living animals, parasitical in, 

 and living upon, the absorbed nutriment taken in by the insect or 

 worm for its own special use. They have neither head, eyes, mouth, 

 organs of locomotion, digestion, circulation, nor sense. They are 

 simple cells, containing a nucleus and an albuminous fluid with 

 granules called sarcode. They move about by means of wave-like 

 undulations of their cellular bodies. Fig. 10 (p. 22), taken from 

 the "Icones Histiologicae" of the celebrated Professor of Anatomy 

 at Wurzburg (A. Kolliker), shows one of these minute organisms 

 largely magnified. 



I have given only one of the forms of this singular animal, but it 

 is often round, sometimes oval! It is colourless and microscopic. As 

 to size, if we take a fine needle and make the smallest mark visible 

 to the naked eye, we should fail in giving any idea of its minuteness. 

 It is quite invisible to the naked eye. I do not find any measure- 

 ments given by authors. These figures, therefore, which illustrate 

 this chapter, are all enlarged from the microscopic high-power image 

 for the purpose of illustration. 



Since the Gregarince were discovered and described by Dufour in 



