278 HETEROGENETIC ORIGIN 



might be seen revolving within their cysts. Some of this batch of 

 Rotifers' ' eggs ' were seen to be filled with such spherical masses, 

 whilst others were observed in which a few of the embryos had 

 escaped from their cysts, and were swimming about as well- 

 marked specimens of Oxytricha, within the thin investing membrane 

 of the Rotifer egg." 



Unfortunately, nothing was stated, either in my note-book or in 

 the work itself, as to the conditions to which these eggs had been 

 subjected, and it was my quest in this direction, resumed about 

 four years ago, that finally led to the discovery of the origin of 

 Otostomata and of Vorticellas, as well as to the repetition of my 

 observations concerning the heterogenetic origin of Oxytrichae, 

 from Hydatina eggs. 



In the spring of 1901 I began to subject Hydatina eggs to 

 different conditions in the hope of again bringing about this 

 transformation into Oxytrichae. After many unsuccessful attempts, 

 I at last found, early in the month of May, that what seemed to be 

 the way to obtain this change was to place portions of Euglena 

 pellicle containing the Hydatina eggs (or else twenty or more eggs 

 carefully scraped with a scalpel from the side of a glass vessel on 

 which they had been laid) in some water in a small earthenware 

 pot, in the manner already described. This final clue was obtained 

 with a very small quantity of remaining material, and unfor- 

 tunately owing to the previous setting in of dry weather, and the 

 consequent drying up of my sources of supply of Euglenas, I was, 

 much to my regret, unable to carry on the investigation.' Still, 

 examination of the small amount of material enclosed in this last 

 pot revealed, on the fourth day, a ruptured Hydatina egg-case, 

 within which were three spheres exactly similar to what I had seen 

 in 1872, and which on measurement proved to be also about -nrrir" 

 in diameter. One of these spheres contained a small Ciliate then 

 actively revolving within its cyst ; and in addition to the spheres 

 there was a small free Oxytricha moving about within the egg-case. 

 The movements of these organisms were arrested with a dilute 

 iodine solution in order that they might be photographed ; but 

 unfortunately this led to the dissolution of the free Embryo 

 Oxytricha, owing to its substance being so delicate, and it is 



' At other times it was tlie long continuance of very wet weather which made 

 it impossible for me to obtain supplies of Euglenas with Hydatin£e. A moderate 

 amount of rain, followed by some days of bright weather, is most favourable for 

 obtaining supplies. 



