1889.] MICROSCOPICAL JOURNAL. 153 



things an organic food-stuft", to be devoured in its turn b}^ our Amceba. 

 Now the bacteria can make their protophism out of mineral matter. 

 Whether we, therefore, consider the nature of the food, or the manner 

 of taking it into the body, Amoebae present a very marked advance upon 

 bacteria. 



C. ABSORPTION. 



Again, here is a slight advance. In bacteria this function is blended 

 with that of digestion. But here, after the food has been digested, and 

 whilst it is passing through the protoplasm, or endosarc of the AmcEba, 

 the endosarc that immediately surrounds the food particle as it goes on 

 its way must absorb nutritious parts and transmit them to the distant 

 regions of the protoplasm. Thus, even here, far down in the animal 

 kingdom occurs a simple rudimentary but distinct act of absorption. 



e. RESPIRATION. 



All that applies as to the breathing of bacterium is found in Amoeba. 

 The respiratory organs are the whole body surface. No special part is 

 yet devoted to the function of breathing. By the whole surface, O is 

 taken in and C O^ given out. And here it will be well to pause for a 

 moment and call the attention of the student to a great principle. The 

 lower w^e descend in our study of living things the more do we find 

 every function performed indifferently bv every part. Nothing is spe- 

 cialized. The whole body of cells breathes, reproduces. But as we 

 ascend in our studv, certain parts of the body take to themselves certain 

 definite functions, and the higher we ascend the more complex- is this 

 " physiological division of labor." 



But whilst bacterium only breathes by its general surface Amcpba has 

 a special organ for respiration. If the Amoeba be carefully watched 

 for awhile in the ectosai'c region, a contraction and expansion occurring 

 consecutively will be seen, as if a round window were opening and 

 shutting in steady succession. Now there is a clear round space in the 

 ectosarc, and now the space is lessening and lessening until it becomes 

 a mere speck, and at last has disappeared altogether. Presently, at 

 exactly the same spot, the mere speck will reappear and gradually en- 

 large until it is a clear round space once more. This space contracting 

 and expanding is called the contractile vesicle. As it contracts, it 

 would seem as if lines radiated from it into the surrounding sarcode or 

 protoplasm. This much is certain. That which follows is not so as- 

 sured. But probably this system of a central space and of canals pos- 

 sibly radiating thence into the protoplasm around is full of water that 

 has air dissolved in it ; and probably the system communicates with the 

 exterior so that the water can be changed. These probabilities are based 

 on the knowledge of certain facts known in connection with kindred 

 structures in higher animals. If, then, we have here a pulsating cent- 

 ral vesicle with radiating spaces passing thence, and if the whole sj'stem 

 contains water holding air in solution, it is possible that thus oxygen is 

 given up to the living active protoplasm into the midst of which the 

 water is pumped, and that the carbon dioxide, that is the chief product 

 of its waste, is removed thence. It is on these grounds that the con- 

 tractile vesicle is regarded as respiratory. Sometimes this structure 

 appears to consist of two or more vesicles that contract as the canals 

 radiating from them expand. 



