720 PROTOZOA. 



to be encysted). The protoplasm seems to collect in one part of the cyst 

 and to break up into minute nodules. These nodules, which are called 

 spores, raise up the outer surface into prominences, and finally, when 

 mature, pass through the wall of the cyst, develop whips of their own, and 

 swim about freely as young individuals known as ** swarm spores." 



Leaving now for a moment those Protozoa, which are rising higher and 

 higher in the scale of organic life, we must notice a group which shows 

 curious degeneration, the Gregarinse. These creatures 

 The Gregarinae. possess neither pseudopodia nor flagella : they can only 

 move very slowly by a kind of contraction of the proto- 

 plasm just below the outer surface, which, being somewhat different from 

 the rest of the body, we may call the "skin." These animalcules are all 

 parasites, hence their degradation. They have managed to get into the 

 bodies of animals higher than themselves, and are able to draw in as 

 food, through the whole surface of the body, the juices of their "host" 

 without any exertion on their own part, They are very common in the 

 bodies of all classes of animals from the worms upward, each kind of 

 Gregarina having its own special feeding ground in some part of a 

 higher animal. One species, for instance, is only found in the gills 

 of a small Crustacean, another in the liver of the Rabbit, and so on. 

 The only kind of outward appendages ever found in these creatures 

 are hooks which enable them the better to attach themselves to their 

 victims. The chief life activity in these, as in most other parasites, 

 is reproduction, which takes place by spore-formation. Two or more of 

 the worm-shaped Gregarinse fuse together, become encysted, and, after a 

 time, produce spores, which are released by the bursting of the cyst. Each 

 spindle-shaped spore develops into an independent individual, being sup- 

 plied by its immediate surroundings with appropriate nourishment. 



We pass on from these degenerate creatures to the highest of the Pro- 

 tozoa, the Infusoria, so-called on account of being found in infusions i.e., 

 in water in which decaying animal or vegetable matter 

 The Infusoria. has been soaked, and in which it was at one time thought 

 that they bred spontaneously. 



In the Infusorians the protoplasm of the body shows more variety than 

 in any other Protozoans. Not only is the outer surface of the body dis- 

 tinctly unlike the inner protoplasm, but it is more or less covered with very 

 fine hairs or cilia (literally eyelashes), which promote its motion. It is 

 sometimes provided with hooks or bristles as well, by means of which it can 

 creep or hang on to other objects. At one definite spot there is a simple 

 mouth, from which a depression often leads into the interior of the body. 

 The mouth is usually encircled by cilia, which, by their rapid vibrations, 

 keep up a kind of whirlpool, and bring particles of food within reach. As 

 the food, which passes on into the body along the tube, is absorbed, definite 

 streamings in certain directions can be made out in the granulated proto- 

 plasm. The indigestible portions of the food are, in some forms, ejected at 

 a definite part of the body. The nucleus is not always round it may be 

 horse-shoe-shaped, or ribbon-like, or it may even resemble a string of beads. 

 There are often several contractile vesicles. 



The Infusoria are very plentiful in fresh water : they prey upon each 

 other, and sometimes upon higher animals, such as Rotifers. Some are 

 parasites. 



There are Ciliated Infusorians and Tentacled Infusorians. 



