502 THE BEGINNINGS OF LIFE. 



fusoria. Thus, speaking of Rotifers, Pritchard says ' : 

 c They are only to be found when the first stage of 

 decomposition has passed away, and they usually dis- 

 appear again when the water becomes putrid and 

 offensive. After the Monadinia, Paramecia, and other 

 smaller Infusoria have run their course and in large 

 measure disappeared, the Rotatoria occupy their places.' 



I have myself been able to follow all the stages of 

 one of the transformations, referred to by Dr. Gros, 

 since I have seen many specimens of encysted Vorticellie 

 become converted into embryo Rotifers. The stages 

 by which this metamorphosis was effected seemed to 

 be very simple, though their real nature and the cause 

 of the several changes was wholly inexplicable. 



The phenomena were first observed under the fol- 

 lowing circumstances. A small portion of Vaucheria 

 having been exposed to sunlight, in a beaker, for several 

 days during the month of June, was afterwards kept in 

 the shade and at a slightly lower temperature (about 

 75 F) for two days. When some specimens of it were 

 examined microscopically, a large number of fine Vorti- 

 cellae of the striated variety were seen attached to the 

 filaments. Other specimens of encysted Vorticellse also 

 existed by the side of the filaments. Some of the latter 

 were spherical and presented the usual finely-granular 

 appearance , whilst others, similar in size, had assumed 



1 Infusoria, 4th ed., p. 652. 



