REPRODUCTION OF PROTOZOA. 115 



the species is sustained, peculiarities or pathological variations of one 

 individual being counteracted by other characters in the neighbour 

 (apparently no near relation) with which it conjugates ; or we may see 

 in it a source of variation as the result of new combinations among 

 the essential hereditary substances. The researches of M. Maupas 

 have thrown much light on the facts, and some of his results deserve 

 summary. 



It has been often alleged that the subsequent dividing is accelerated 

 by conjugation ; but Maupas finds that this is by no means the case. 

 The reverse in fact is true. While a pair of Infusorians (Onychodromtts 

 grandis] were engaged in conjugation, a single individual had, by 

 ordinary asexual division, given rise to a family of from forty thousand 

 to fifty thousand individuals. Moreover, the intense internal changes 

 preparatory to fertilisation, and the general inertia during subsequent 

 reconstruction, not only involve loss of time, but expose the Infusorians 

 to great risk. Conjugation seems to involve danger and death rather 

 than to conduce to 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 pustulata), and observed its generations till March 1886. 

 By that time there had been two hundred and fifteen generations pro- 

 duced by ordinary division, and since these lowly organisms do not 

 conjugate with near relatives, there had been no conjugation. 



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

 observed to have exhausted itself. The members were being born old 

 and debilitated. The asexual division came to a standstill, and the 

 powers of nutrition were lost. 



Meanwhile, before the generations had exhausted themselves, several 

 of the individuals had been restored to their natural conditions, where 

 they conjugated with unrelated forms of the same species. One of 

 these was again isolated, and watched for five months. In this case, 

 up till the one hundred and thirtieth generation, it was found that on 

 removal to fresh conditions the organisms were capable of conjugating 

 with unrelated forms. Later this power was lost, and at the one 

 hundred and eightieth generation the individuals of the same family 

 were observed making vain attempts to conjugate with each other. 



We thus see that without normal conjugation the whole family 

 becomes senile, degenerates both morphologically and physiologically. 

 Morphologically, the individuals decrease in size, until they measure 

 only a quarter of their original proportions, the micronucleus atrophies 

 completely or partially, the chromatin of the macronucleus gradually 

 disappears, other internal structures also degenerate. Physiologically, 

 the powers of nutrition, division, and conjugation come to a standstill, 

 and this senile decay of the isolated individuals or family inevitably 

 ends in death. 



The general conclusion is evident. Sexual union in those Infusorians, 

 dangerous, perhaps, for the individual life, and a loss of time so far as 

 immediate multiplication is concerned, is absolutely necessary for the 

 species. The life runs in strictly limited cycles of asexual division. 

 Conjugation with allied forms must occur, else the whole life ebbs. 

 Without it, the Protozoa, which some have called "immortal,'' die a 



