SMALL MASSES OF ZOOGLCEA 193 



the proper focal distance, appearances such as are represented in 

 Fig. 24, B, C ( X 500), are to be observed. That is, the pellicle in 

 these situations is seen to be pretty closely packed with a number 

 of minute, motionless, and rather ill-defined whitish corpuscles, 

 which are almost always found to be located in the under layer of 

 the pellicle. 



I have over and over again noticed these appearances in the 

 pellicle, and even more distinctly as in Fig. 22, D, owing to the 

 corpuscles being more fully formed, when there was not a single 

 active Monad or Amoeba in or around the portions under examina- 

 tion. But when other portions of the same pellicle have been 

 examined, twelve to sixteen hours later, thousands of active Monads 

 have been present, all of about the same size as the motionless 

 corpuscles previously seen to be forming, and each moving more 

 or less rapidly by means of a single flagellum. These active 

 Monads, such as are shown in Fig. 22, E (x 500), are to be found, 

 not only around the portion of the pellicle under examination, 

 but beneath it where previously only motionless corpuscles 

 existed. 



For a long time, owing to the discrete corpuscles in their motion- 

 less condition being situated on the under surface of the pellicle, 

 I found it very difficult thoroughly to satisfy myself as to 

 their actual mode of origin. The general indications were 

 certainly strongly in favour of their having been formed in 

 and from the pellicle itself, as may be gathered from the 

 following considerations : — 



(i) Thousands of Monads appear comparatively suddenly of full 

 size, and often when their appearance has been seen to be preceded 

 by the gradual formation of multitudes of motionless corpuscles of 

 the same size in the under layers of the pellicle. 



(2) Never in their motionless condition, and only veiy rarely in 

 their free active state, was any evidence of multiplication by fission 

 to be seen, although many thousands of these Monads have been 

 examined from time to time. 



(3) In the course of five or six days, when the weather is warm, 

 Monads are in some pellicles formed in enormous numbers, and 

 obviously at the expense of the pellicle itself, since whole regions 

 of this membrane actually disappear where they have been formed, 

 leaving only intervening ridges in the midst of which other motion- 

 less corpuscles appear to be forming.' 



' This is shown in " Studies in Heterogenesis," PI. VI., Fig. 54, D, 



13 



