310 Dallinger, Drysdale's u. Dallinger's Untersuchimgeu an Biflagellaten. 



of apparatus for keeping- the organisms alive continuously under close 

 observation; and the combination of these things is by no means rare. 

 But the difficulty begins when we have to follow the organisms into 

 the more obscure, and relatively less common phases of their life- 

 cycles, always supposing that our observations are made upon the 

 living and active organism. It becomes a task impossible, in my 

 judgement, save to joint observation. Over and over again given 

 observations fail from many causes, and there is no way open but to 

 begin again. 



You may have noted that we expressed this opinion many years 

 ago; its importance was indeed stated in our very first paper l ) ; where 

 the need of continuous observation is enforced by an example. 



Now in the accompanying rough sketch taken from my folio, 

 A represents what we called a ,,cercornonad" in the earliest condition 

 prior to the act of fusion. B represents the same organism when 

 the act of fusion (of two) is almost complete. 



Let it be supposed that we 

 obtain material from a macera- 

 tion containing this organism in 

 great abundance, and in some 

 approved way dry on a slide a 

 lesser or larger group of these 

 forms, and then stain them. The 

 process of shrinkage and distor- 

 tion, and the inevitable changes 

 will make it difficult indeed to 

 discover that they are not alike, 

 o s7 that a whole series of changes 

 has occurred in B, which have 

 never existed in A , and that 

 they are morphologically and 

 physiologically entirely different. 

 But by following A into 

 fusion with another (never 

 a matter that can be done 

 without difficulty and enduring patience) and seeing the blending forms 

 reach the condition of B, we become provided with unmistakable evidence. 

 Again in the 1878 paper in the Proceedings of the Royal Society 

 ,,0n the life -history of a minute septic organism", we are provided 

 with another instance. In the sketch C represents a state of fission: 

 but D gives a drawing of a condition of fusion in the same organism. 

 The manner in which the intermediate stages took place would never 

 have been (in our hands) discovered by means of dried and stained 



1) Monthly Microsc. Journ., Vol. X, p. 55. 



