CHAPTER XIII 



THE HETEROGENETIC ORIGIN OF CILIATED INFUSORIA (CONTINUED) 



(e) On the Transformation of the Immature Eggs of a 

 Gnat-like Fly into Ciliated Infusoria. 



WHILE studying the changes that occur in the scum on 

 an egg and water emulsion, in the summer of 1900, I 

 occasionally found on the surface of the fluid, within thirty-six 

 hours of its being prepared, a small grey fly with monilated, hairy 

 antennae, which, as I subsequently learned, belonged to the genus 

 Psychoda. On July 4 of that year I had the curiosity to examine 

 under the microscope one of these flies which had died on the 

 fluid. I put it into a drop of water, placed a cover-glass over 

 it in the ordinary way, and on examination found that the weight 

 of the latter had ruptured the abdomen, and that a great swarm 

 of minute spherical or ovoidal Ciliated Infusoria were pouring out 

 from the abdominal cavity, while an equally large number were to 

 be seen swarming about within the abdomen, mixed with other 

 bodies apparently similar except that they were motionless. 

 Fig. 57 shows a few of the Ciliates, which emerged from the 

 abdomen, after they had been killed by a weak solution of iodine. 

 One, near the centre, may be seen to be very much larger than the 

 others. 



Each summer since, during the month of July, except in 1903 

 when that month was unusually wet and cold, I have found other 

 specimens of these flies and many of them have contained the 

 same kind of Ciliates — sometimes as many as two or three hundred 

 within a single fly. The flies have only appeared on the fresh egg 

 emulsion when the temperature of the air has been for some days 

 at or above 70° P., and they have been found on the emulsion long 

 before any Ciliates appeared therein. ' The flies containing the 



' Sometimes I have only been able to obtain specimens towards the end of 

 July, on account of the weather being unfavourable, and as during August I have 



