POLYTOMA 175 



gradually diminish in size, and finally they disappear and the 

 animal dies. The- exact mode of formation of these starch 

 granules is not understood. They are not ingested after the 

 manner of the starch grains swallowed by Bodo angustatus, for 

 Polytoma has no mouth, and has never been seen to ingest soHd 

 particles, nor are any foreign matters excepting these starch 

 granules to be seen in its protoplasm. Its nutrition must be 

 described as saprophytic, for it lives immersed in a nutrient 

 fluid, and imbibes it by the whole surface of its body. It 

 evidently does not get its carbon from carbon dioxide, for, as 

 we have just seen, it becomes enfeebled and dies if it is taken 

 from the nutrient solutions in which it lives, and therefore it 

 must form starch in some other manner than its chlorophyll- 

 containing relatives. Now, in the higher animals a form of 

 amylum, known as glycogen or animal starch, is found in some 

 abundance in the liver and in muscle. Numerous experiments 

 have shown that glycogen is formed, in the dog for instance, 

 when the animal is kept on an exclusively proteid diet, and it is 

 therefore proved that starch may be formed by the activity of 

 living tissue from proteid material. It cannot be doubted that 

 the protoplasm of Polytoma has this same power of converting 

 the albuminous substances which it absorbs from organic 

 solutions into starch. Attention should be paid to the existence 

 of starch in Polytoma uvella, for it is sometimes incorrectly said 

 that organisms devoid of chlorophyll never contain starch. 

 Polytoma reproduces itself by a process of continued division 

 within the cell envelope, either in the free swimming or in a 

 resting condition. The act of division may nearly always be 

 seen in individuals which are kept under continuous observation. 

 In a free swimming form the nucleus divides mitotically, and a 

 transverse constriction of the protoplasmic body follows, not 

 involving the envelope. The two flagella of the parent form 

 remain attached to the anterior product of division and the 

 organism continues to swim about actively, consisting now of 

 two cells lying inside a common membranous envelope, the 

 more anterior of the two cells alone bearing flagella. The next 

 di^vision is at right angles to the first, and therefore parallel to 

 the long axis of the original parent cell. Four cells are thus 

 produced, still enclosed within the envelope of the original 

 parent form, and still the two flagella are active and attached to 

 one only of the four daughter cells. Another division may 



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