246 HETEROGBNETIC ORIGIN 



by a glass shade, which was allowed to overlap the edge of the 

 mantelpiece, so as to permit access of more air to the Euglenas than 

 they would otherwise have had. 



When examined three days later, a thin scum, composed in the 

 main of small Euglenae, was found on the surface of the fluid. A 

 few of these organisms were seen to be becoming decolourised, 

 and exhibiting different stages of the process. They were all 

 motionless, round or oval, and of just the same varying size as the 

 unaltered Euglenae among which they were situated. During my 

 examination of this pellicle, many flagellate Monads and Rotifers 

 were seen ; but no Ciliates of any kind were met with. Two days 

 later the decolourised Euglenas were found to be still more 

 numerous, while many of the unaltered Euglense were slowly 

 rotating within their thin and scarcely visible cysts. Twenty-four 

 hours later, that is, on the sixth day after gathering the EuglenEe, 

 I found a few of the decolourised specimens showing traces of the 

 formation of the characteristic buccal cyUnder of a Nassula, and a 

 few days later I saw such Ciliates revolving within, and issuing 

 from, their cysts. 



These several stages of the transformation may be illustrated by 

 the photographs comprised in Fig. 53. Thus, a group of five 

 Euglense in different stages of decolourisation is shown in 

 A (x 375)- In the two lower specimens the change is most 

 advanced, and in the one on the left it was complete except for 

 one small mass of the green substance. B (x 375) shows three 

 other Euglenae completely decolourised, except for a few green 

 granules remaining, together with a vestige of the red eye-speck in 

 the upper specimen. That on the right shows a small vacuole ; 

 but in neither of them is any trace of the buccal tube or of a 

 nucleus to be seen. In C ( x 375) the first rudiments of the buccal 

 tube are to be seen appearing in two of these transformed 

 Euglense, and in another specimen, in which the tube seemed to 

 be in about the same stage of development, an ovoid nucleus was 

 seen, though I did not succeed in photographing it satisfactorily. 

 D (x 375) shows one of these Ciliates, which was killed by a very 

 dilute formalin solution, just after its emergence from one -f the 

 cysts. It seems large in proportion to the size of the cyst from 

 which it has escaped — as is generally the case both with Ciliates 

 and with Rotifers. It bears, however, the usual marks of im- 

 mature development. This is indicated by its delicate texture, and 

 by the scanty development of a few weak Cilia about its anterior 



