THEORY OF FERTILISATION. 165 



and reconstruction, two "slipper animalcules" fertilise one 

 another. What is the meaning of all this? 



Each infusorian, after conjugation, proceeds to divide, but 

 the results are to all appearance the same as it previously pro- 

 duced. There is no special sexually produced generation. 



It has been often alleged that the subsequent dividing is 

 accelerated by conjugation ; but Maupas finds that this is not 

 so. The reverse in fact is true, — it is a loss of time. While a 

 pair of infusorians [Onychodromus grandis) were indulging in a 

 single conjugation, another had become, by ordinary asexual 

 division, the ancestor of from forty thousand to fifty thousand 

 individuals. 



Moreover, the intense internal change preparatory to fer- 

 tilisation, and the general inertia during subsequent reconstruc- 

 tion, not only involve loss of time, but expose the infusorians 

 to great risk. It seems then like a condition of danger and death 

 rather than of multiplication and birth. 



The riddle was, in part at least, solved by a long series of 

 careful observations. In November 1885, M. Maupas isolated 

 an infusorian {Stylonichia picstulata)^ and observed its genera- 

 tions till March 1886. By that time there had been two 

 hundred and fifteen generations produced by ordinary division, 

 and since these lowly organisms do not conjugate with near 

 relatives, there had, of course, been no sexual union. 



What was the result ? At the date referred to, the family 

 was observed to have exhausted himself. They were not old 

 exactly, but they were being born old. The asexual division 

 came to a standstill, and the powers of nutrition were also lost. 



Meanwhile, however, several of the individuals, before the 

 generations had exhausted themselves, had been removed to 

 another basin, where they conjugated with unrelated forms of 

 the same species. One of these was again isolated, and watched 

 for five months. The usual richness of successive generations 

 occurred ; members removed at different stages were again 

 observed to conjugate successfully with unrelated forms, and 

 this was done on to the one hundred and thirtieth generation. 

 After that, however, the family being again near its end, the 

 removal was no longer any use. About the one hundred and 

 eightieth generation, the strange sight was seen of individuals 

 of the same family attempting to unite with one another. The 

 results were, however, 7iil, and the conjugates did not even 

 recover from the effects of their forlorn hope. 



