THE LOWER FORMS OF LIFE. 



29 



interior of the animalculse, and carried into the fluid sarcode, is a 

 constant circulation from left to right ; round the general cavity are 

 numerous granules of chlorophylle, which give it a green colour, and 

 which we have seen before is the pigment of vegetable structure, 

 and is always floating about in water. Now let us turn the little 

 creature over upon its back, and notice what comes into sight as 

 shown in Fig. 25. At a we have the mouth, and at b the gullet 

 but mark, no stomach. The gullet simply carries the food into the 

 bag, which is inclosed by the " cortical layer," and in which the 

 liquid sarcode circulates, carrying with it the particles of food, 

 chlorophylle, granules, &c. 



a 



c 



Fig. 25. 



Fig. 26. 



Fig. 25. Ventral side of Paramsscium Bursaria, showing a, the stomach b, the gullet or 

 oesophagus c, the nucleus d, the nucleolus. 



Fig. 2G.Paramiecium Aurelia (after Kolliker), dividing a a, contractile chamber 6, elon- 

 gated nucleus contracting in the middle c c, nucleolus divided, but the new ones still 

 connected with each other. 



In Fig. 26 we have an illustration of one of the methods by which 

 Infusoria increase. The nucleolus divides into two, and each division 

 attaches itself to the ends of the nucleus, the latter becoming at the 

 same time elongated. The animalcule and nucleus are observed to 

 become thinner in the middle, and ultimately they divide into two 

 distinct animalcules, which again subdivide, and so increase and 

 multiply. It has recently, however, been discovered by M. Balbiani, 

 and confirmed by Stein and Kolliker, that the Infusoria are also 

 reproduced by the following means. The nucleolus (c, Fig. 18, p. 27) 

 represents the male part of the creature, just as the pollen grain 

 does of the plant ; while the so-called nucleus (b) is the ovary. At 

 certain seasons the nucleolus is observed to grow in size ; and in 

 this condition two animalcules become conjoined, as shown in the 

 Gregarinse, and, mingling together, the nucleolus of each division 



