302 APPLIED BIOLOGY 



masses (called food-vacuoles) move around as indicated by the 

 arrows in the figure; digestive juices in the paramecium slowly 

 dissolve the digestible food ; the protoplasm absorbs the dissolved 

 foods, and the indigestible remains (such as hard parts of some 

 small animals and plants often eaten, or the carmine particles in 

 above experiment) are ejected at a soft spot in the cell-membrane, 

 as shown just below the gullet in Fig. 88, B. 



Using the high-power objective, examine the cilia carefully. 

 Look for the two clear spots shown in Fig. 88, A ; they are spaces 

 in the protoplasm filled with water, and when the surrounding 

 protoplasm contracts the contents are ejected through a little canal 

 leading out of the body. They are excretory organs, known as con- 

 tractile vacuoles or pulsating vesicles, and the water they eliminate 

 contains some nitrogenous excretions. Sometimes they pulsate as 

 regularly as the heart beats in higher animals. 



The small spindle-shaped bodies seen near the cell-wall in the 

 Figs. 88, A and B, contain long threads which are thrown out when 

 the animal is irritated by chemicals or by pressure. Their purpose 

 is believed to be defense against other lower animals. Some of 

 these threads, much longer than cilia, are shown in the lower part of 

 Fig. 88, B, trch. 



Stained preparations should be examined for the nucleus. A 

 small nucleus (paranucleus) lies near the main nucleus. 



Division. Some of the paramecia seen swimming may be 

 constricted near the middle of their bodies, as if an invisible 

 thread were tied around them. This indicates approaching 

 division, and such a specimen should be watched as the con- 

 striction grows deeper, and finally the animal is completely 

 divided into two new and young individuals which swim 

 independently. The parent animal merges its own individu- 

 ality into that of its two equal offspring. Contrast this with 

 higher forms, as the frog, which produce young, while the 

 parent continues to live until it grows old and dies. It is 

 evident that, barring accidents and disease, there is no chance 

 fdr a paramecium to grow old and die ; for when it grows 

 old, it simply divides into two young animals, which in turn 

 take food, form new protoplasm, grow to the full size, and 

 divide. This is the characteristic method of reproduction 



