OF CILIATED INFUSORIA 257 



take place in the dark or not, as well as the question of the genus 

 to which the Ciliates which are thus originated belong, must for the 

 pi-esent be left undetermined, as my supply of the lichen from 

 which these particular ' Sloths' were derived was exhausted.' 



These changes in the eggs of the Macrobiotus are very interesting 

 in another respect — seeing that they will take place beneath a 

 cover-glass, though it is extremely difficult to obtain evidence 

 that the closely-allied heterogenetic changes which I have seen 

 occurring in the eggs of certain Rotifers will occur under similar 

 conditions. 



That we have here again to do with a definite process of 

 Heterogenesis seems perfectly clear, as a consideration of the 

 following facts will show : — 



(i) The Macrobiotus has only a small suctorial mouth, and the 

 general envelope of its body is tough and resistant. 



(2) No Ciliates can ever be seen attempting to penetrate from 

 without. 



(3) The Ciliates have only been found in female ' Sloths ' which 

 had previously contained eggs. 



(4) The Ciliates, as first seen, are large but slowly-moving 

 embryos of the same size as the eggs — like those that were found 

 in the specimen represented in Fig. 56. 



(5) It would be quite impossible for large embryos of this 

 kind to penetrate from without, through the tough integument 

 of the ' Sloths.' 



' In the following year I tried to repeat these observations, and again brought 

 some of the same kind of Lichen from the Pyrenees, though from another 

 locality. Unfortunately, however, it contained only a very few immature 

 specimens of this 'Sloth.' Not a single one containing eggs was found. Another 

 species, M. Hiiflandii, has since been found in a pond at Northwood in associa- 

 tion with masses of Oscillatorias. These creatures contained plenty of eggs, and 

 15-20 were occasionally seen in their cast-off coats. Though a few trials were 

 made with such eggs, none of them went through changes similar to those just 

 described. 



17 



