436 Gary N. Calkins. 



acknowledge the friendly and scientific interest which prompted 

 these suggestions, and desire to state that if they were not always 

 carried out, it was because of the limits of my time and of the con- 

 stantly decreasing number of individuals left to experiment with. 

 It was my desire to try as many classes of experiments as possible, 

 and some of these might have been successful if tried at an earlier 

 time or if carried out on a sufficiently large scale, but here again 

 the scarcity of living material would not allow the continued 

 experimentation along lines that were fruitless on the first trial. 

 It must be remembered that such experiments, to be of any value 

 in a work like this, had to be made on the material that had been 

 under constant observation for nearly two years, and preliminary 

 experiments with fresh forms from the ponds were valueless so 

 far as indicating the effect on the vitality of the race under 

 observation. 



III. PROTOPLASMIC STRUCTURES OF PARAMCECIUM. 

 I. The Norrnal Paramceciutn. 



The usual size of a normal Paramcecium is from 200 to 300 

 microns, and the form is fairly constant, warranting the designa- 

 tion "slipper animal." In all of the preserved specimens that I 

 have made from time to time, the fixing fluid was saturated cor- 

 rosive sublimate to which was added 10 per cent of glacial acetic 

 acid. Having a common method of fixation the different indi- 

 viduals can be compared point by point. 



a. The Endoplasm. The endoplasm of a normal form is made 

 up of various granules of diff'erent sizes, of vacuoles and crystals 

 (Fig. i). When the animal is moving about in a nutrient 

 medium it constantly takes in food with the water absorbed. 

 The food of Paramcecium consists of bacteria, and these accumu- 

 late in a gastric vacuole until the latter has attained a certain size 

 when, according to Wallengren,^ it is caught up in the endo- 

 plasmic flow and carried to the posterior end of the body. It then 

 moves anteriorly toward the left side, ultimately passing over to 

 the right and then down on the right side. In this migration of 



^ H. Wallengren. Inanitionserscheinungen der Zelle. Zeit. f. Allg. Physiologie 

 I.. 1, 1901. 



