162 THE MICROSCOPIST. 



digestive sacs made by the inclosure of food by the soft 

 bioplasm. 



In addition to the "vacuoles" described, contractile 

 vesicles are seen which contract and dilate rhythmically, 

 and do not change their position. They have been con- 

 sidered to serve for respiration. 



Most of the Infusoria multiply by self-division (Plate 

 XIII, Fig. 119), and at certain times undergo an encyst- 

 ing process, much resembling the " still " condition of Pro- 

 tophytes, and like that serving for preservation under 

 circumstances which are unfavorable to ordinary vital 

 activity. The gemmules or progeny which result from 

 the bursting of the cyst do not always resemble the parent 

 in form. The recent researches of Drs. Dallinger and 

 Drysdale have shown considerable variety in the life his- 

 tory of the Infusoria. In some instances the product of 

 the encysting process was not a mass of granules, but an 

 aggregation of minute germinal particles not more than 

 sWotJoth f an i ncn i n diameter, and capable of resisting 

 heat, either by boiling or by dry heating up to 300 F. 



The observations of M. Balbiani show that in many of 

 the Infusoria, male and female organs are combined in 

 the same individual, but that a congress of two is neces- 

 sary for the impregnation of the ova, those of each being 

 fertilized by the spermatozoa of the other. 



There is also a curious tribe of suctorial animalcules 

 called Acinetce, which put forth tubular prolongations 

 which penetrate the bodies of other species and grow in 

 their interior as parasites. 



The systematic arrangement of the Infusoria is yet 

 unsettled. Ehrenberg's families, excluding those now 

 placed among Algse or Rhizopods, are as follows : 



