DALLINGER AND DRYSDALE. I 33 



four days. The six vessels left uneovered from the commencement being 

 successively examined, were found in every instance to be abundantly 

 peopled with both of the two monad forms present in the evaporizcd 

 infusion, and developed from the germs diffused as dust through the air of 

 the experimental chamber. Two days later a similar examination was 

 made of the four remaining vessels which had remained covered, and with 

 somewhat different results. In all these the Springing Monad was abun- 

 dantly developed, but the Calycine form was found in only one of the 

 receptacles, and then in very small numbers. 



At first, this result appeared perplexing, but it occurred to Mr. DalUnger 

 that the spores or germs of the last-named type, as in the case of the adult 

 monad, were considerably larger than those of the former, and had, on account 

 of their greater specific gravity, fallen to the bottom of the chamber before 

 the removal of the covers from the four vessels last examined, and had thus 

 been excluded from developing ; this inference was fully substantiated by a 

 repetition of the experiment with certain modifications. On this occasion, the 

 material used was the desiccated residuum of an infusion containing abun- 

 dantly, in its sporiform condition, the simple uniflagellate type, Monas Dallin- 

 geri, the smallest species yet met with by him, and whose adult length did not 

 exceed the i -4000th or 1-45 00th part of an English inch. The spores or 

 germs produced by this animalcule were correspondingly minute, and it was 

 consequently surmised that they would remain floating in the still air of the 

 experimental chamber long after the subsidence of the germs of the larger 

 types, and develop in vessels placed there for their reception at a later date. 

 Finely pulverized and intimately mixed with material containing the larger 

 Calycine Monad {Tetrainitus rostratus) having an adult length of T^iij- to 

 t"o'(Jit"> these most minute germs were dispersed as before in a prepared 

 chamber. At the end of four hours and a half, nine small glass basins 

 were introduced, three of them remaining open and six being temporarily 

 covered. At the end of twenty-four hours two of these covered vessels were 

 exposed to the air of the chamber, and at the expiration of forty-two hours 

 the remaining four were similarly exposed. After each set had been left 

 undisturbed for five days they were examined with the following results. 

 The first three (without covers) contained both descriptions of monads 

 in every drop out of the sixty examined. The next two, uncovered at the 

 end of twenty-four hours, were found in every instance to contain the 

 smaller uniflagellate monad in abundance, but the larger one in a single 

 drop only out of the total of sixty examined. In the remaining four 

 vessels, uncovered after a lapse of forty-two hours, the result was that 

 the smaller type was found abundantly in every drop, while the larger one 

 was entirely absent. Finally, after the removal from the chamber of these 

 last four, four more vessels of sterilized putrescible fluid were put in their 

 places, to ascertain if any of the germs of the same type yet remained 

 suspended in the air ; but on examination five days later it was found 

 that not a trace even of this most minute flagellate species was present 



