256 HETEEOGENETIC ORIGIN 



low power ( x 65) and with a short exposure, before returning the 

 slip to the damp chamber.' 



I examined the specimen again after another seven hours, and 

 still found only two Ciliates, though they had grown, and were 

 much more active. Evidence of their previous activity was also 

 afforded by the disordered and fragmentary condition of the 

 remains of the other eggs, and of the internal organs of the 

 ' Sloth.' It was impossible to photograph the Ciliates again in 

 their more active condition, and in my attempt to remove the 

 Macrobiotus from underneath the cover-glass, where there was 

 another specimen that I much wished to preserve, I unfortunately 

 lost it. 



After all, however, the evidence that was wanted had been 

 supplied — the egg of the Macrobiotus had been proved to be 

 converted into a Ciliate. The large stationary egg had become 

 replaced by a slowly moving body of like size, which subsequently 

 proved to be a great Ciliate^ and no smaller Ciliate was ever seen 

 within the body of this animal. The other two steps of the 

 process by which in twenty-four hours such a specimen as is 

 shown in Fig. 55, B, is enabled to yield the appearance repre- 

 sented in C is plain and easy to be recognised — rapid fission of the 

 Ciliate or Ciliates, together with their voracity, will account for all 

 that C represents. 



There is the further noteworthy fact that in various specimens of 

 Macrobiotus that have been under examination, in which there 

 were no eggs, no Ciliates have ever appeared. 



In the specimens shown in Fig. 56 the changes had been very 

 slow in comparison with those shown in Fig. 55 — seeing that after 

 sixteen hours there were in the former specimen still only two 

 Ciliates. This I am disposed to think was probably due to this 

 specimen having been examined three times and photographed 

 three times, while the changes were in progress, instead of only 

 once, as for the specimen whose changes are shown in Fig. 55. 



Still, the restrictive influence of light over these heterogenetic 

 changes occurring in the eggs of Macrobiotus, is altogether slight 

 as compared with the absolute stop which exposure to light puts 

 to the heterogenetic changes occurring in the eggs of Hydatina 

 which I shall presently have to describe. 



Whether these same changes in the eggs of Macrobiotus would 



' This photograph has since been enlarged to its present size. 



