166 ME. F. CT/RREY ON A SPECIES 



becomes attached to the apex of the stem precisely in the spot 

 usually occupied by the vesicle, and it is not always easy for the 

 observer to tell whether he is looking at the vesicle itself or at a 

 substituted drop of water. 



The second appearance alluded to above is not so easy of 

 explanation. In the interior of the drops of water which, as 

 has just been mentioned, sometimes occupy the place of the 

 vesicle, I have several times seen a small orange-coloured body 

 revolving with more or less rapidity, but having rather the ap- 

 pearance of being carried round and round by the force of a 

 current than by any voluntary motion. This, or a similar ap- 

 pearance, was noticed by Ehrenberg, and described by him in 

 a paper published in 1823, in Kruze and Schmidt's 'Mykolo- 

 gische Heffce' ; he did not however ascertain what the revolving 

 body was, and only endeavoured to explain its rotation by attri- 

 buting it to some unknown physical agency which kept the drop 

 of water in perpetual revolution, I was very desirous of ascer- 

 taining the nature of this moving body, and tried to detach it 

 from the drop of water. This attempt was not successful, but I 

 managed to float a drop entire with its orange-coloured occupant 

 on to a piece of white paper, and then waited for the water to 

 evaporate, hoping thus to leave the object high and dry. How- 

 ever, as the water dried up the body became entirely disintegrated, 

 resolved itself into a mass of granular orange-coloured particles, 

 and left nothing behind but a yellow stain on the surface of the 

 paper. As to what its nature may be, or what may be the cause of 

 its singular rotation, I can offer no conjecture, but I have thought 

 it worth while to mention the above facts with the view of directing 

 further attention to this curious phenomenon. It is interesting 

 to notice the resemblance in point of structure between the genus 

 Pilobolus and the fungus which causes the annual epidemic 

 amongst the House Flies ; the only essential difference being, that 

 the latter throws off a single cell, whereas in Pilobolus the cell 

 which is thrown off is the mother-cell of innumerable multitudes 

 of spores, by which the species is reproduced. It is possible, 

 however, that the contents of the single cell in the JEmpusa may 

 become subdivided into smaller reproductive particles after sepa- 

 ration from the parent plant ; and this supposition seems the more 

 probable as the single cell is of too large a size to admit of its 

 gaining access to the bodies of the flies, in the interior of which 

 (according to Dr. Conn's account in a late paper) the first sym- 

 ptoms of this disease are always to be noticed. 



