OF HETEROGENBSIS 219 



on the right the contents of the cyst have been converted, without 

 remainder, into two Peranemata, except that in one of them the 

 pigment of the eye-speck was in part left. These bodies I watched 

 for some time actively moving within their cyst, and the long stout 

 fiagellum of each was distinctly seen before their movements were 

 stopped by a weak solution of formalin. I have also watched many 

 others and have seen them emerge from their cysts as rather large, 

 fully-formed Peranemata. Many of them contain small, differently- 

 coloured pigment masses, which are small unconverted, or partially 

 converted, portions of the substance of the Euglenas from which 

 they have been formed. These organisms never seem, like Amoebas, 

 to take masses of food-stuff into their bodies. 



(i) Transformation of the Substance of Encysted 

 Prorodons into Peranemata. 



The changes now to be described occurred in a number of 

 encysted Ciliates that were found in a tall vessel, filled with 

 water to the depth of about seven inches, into which, six weeks 

 previously, and near the end of the month of October, an abund- 

 ance of Chlamydomonads and Euglenas were placed. The vessel 

 remained during most of this time on a stand outside a window 

 with a south aspect. After about four weeks a scum had grown 

 over the walls of the vessel, which was found to consist to a large 

 extent of a felt-work of algoid filaments, mixed with Oscillatorise, 

 and a number of Euglense. The Euglenae were most abundant in 

 the scum over the lower third of the vessel, while in the upper 

 third, more especially, there were found a large number of active 

 Prorodons (with distinct terminal oral cylinders) mostly gorged 

 with small green corpuscles : other specimens were seen becoming 

 motionless and beginning to encyst ; while a much larger number 

 of them were actually encysted and decolourised — the cysts being 

 very thick, plicated, and without spines or projections of any kind. 



These encysted specimens were searched for and examined at 

 intervals for a period of about three weeks, by which time the 

 supply was pretty well exhausted. The following are some of the 

 facts that were made out. 



The tendency in the great majority of them was to reach a 

 certain stage of reorganisation, and not to advance any further ; 

 the conditions apparently not being favourable to the occurrence 

 of the ordinary changes which these encysted Prorodons were 



