INFUSORIA 49 



the surface which may be shot out into the water. In a few 

 forms (Vorticella] nettle organs are present. The ectosarc often con- 

 tains muscle ridges called myonemes, which appear as parallel longi- 

 tudinal or spiral lines, and in a few cases (Stentor) striated muscle 

 fibrillae are present. The entosarc is more fluid than the ectosarc and 

 is granular and contains a variety of specialized structures. Chief of 

 these are the nuclei, of which two kinds are present, the micronucleus 

 and the macronucleus. The latter is of large size and often branched 

 or irregular in shape, and is supposed to be vegetative in function. 

 The very much smaller micronucleus, of which more than one may be 

 present, lies alongside the macronucleus and is chiefly concerned with 

 reproduction and conjugation. The entosarc also contains one or more 

 contractile vacuoles and food vacuoles. The former have a definite 

 position in the body and serve to eliminate the water taken in with the 

 food vacuoles together with the excretory wastes. The food vacuoles 

 are globules of water which are taken into the entosarc together with 

 the food. 



The food of Infusoria consists of organic particles of all sorts: 

 some live principally on animal food, some on plant food, many are 

 scavengers, and a few are parasitic. In all, with the exception of 

 certain parasitic forms, mouth and gullet are present: an oral groove 

 may lead to the mouth. The anus is usually a temporary opening. 



The Infusoria reproduce by division, the animal in most cases 

 dividing into two equal parts. In some forms division takes the form 

 of budding. Conjugation takes place in all Infusoria. The two conju- 

 gating individuals fuse, in most cases temporarily by the ectosarc of 

 the mouth region, and an interchange of micronuclear substance takes 

 place. The macronucleus disintegrates in each animal while the micro- 

 nucleus divides several times. The products of these divisions disin- 

 tegrate, with the exception of a single one, which divides again. Of 

 the two micronuclei thus obtained in each of the conjugating individ- 

 uals, one migrates across to the other individual and fuses with the 

 micronucleus remaining there. This fusion micronucleus then divides 

 and a portion of it enlarges to form a new macronucleus. Where more 

 than one micronucleus is present, it is probable that this process goes 

 on with all of them. All Infusoria encyst themselves at certain times, 

 in which condition they may be carried by the wind long distances. The 

 Infusoria are found in both fresh and salt water. The name originated 

 with Ledermiiller in 1763 and was at first applied to all minute organ- 

 isms which may appear in infusions. Only in modern times has its 

 use been confined to protozoans. The class, contains about 1,200 species 

 grouped in 2 subclasses, 



