386 



THE INFUSORIA 



The method by which reproduction takes place in the repro- 

 ductive cysts is not known with certainty, but it is probable that 

 there is a rapid succession of simple fissions of the protoplasmic 

 contents of the cyst, leading to the production of numerous swarm- 

 spores, as is stated to be the case in Holophrya multifiliis (Fig. 36). 



CONJUGATION. A single indi- 

 vidual Ciliate Infusorian can pro- 

 duce a large number of generations 

 of daughter individuals by the pro- 

 cess of fission, but there is reason to 

 believe that the number is limited, 



FIG. 35. 



Cyst of Dileptus anser, O.F.M. , 

 provided with an outer shell or 

 ectocyst and an inner mem- 

 brane (endocyst) attached to the 

 ectocyst at the poles. (After 

 Cienkowsky.) 



FIG. 36. 



Cyst of Holophrya midtiJUiis, Fouq., 

 as found at the bottom of aquaria in 

 which fish affected with Holophrya are 

 living. From the cyst numerous cili- 

 ated swarm - spores are escaping. 

 (After Fouquet.) x about 75. 



and that after a time the power of fission slackens and ulti- 

 mately ceases. Under normal conditions, however, the individuals 

 exhibit a tendency to conjugate after several generations have 

 been produced by fission, and if we are justified in regarding the 

 individuality of two conjugating INFUSORIA as the same after con- 

 jugation as before, it may be said that the result of conjugation is 

 a renewal and a stimulation of the powers of fission of the con- 

 jugating individuals. Although our knowledge is still far from 

 complete, it seems certain that a process of conjugation occurs in 

 all HETEROKARYOTA, and that this process is essential for the con- 

 tinuance of the vitality of the species. 



There can be no doubt that the impulse to conjugation is in a 

 large number of cases periodic, the individuals of a swarm showing 

 for several days together no tendency to conjugation, and then 

 simultaneously collecting together in pairs and conjugating. The 

 cause of the impulse is obscure. Maupas expressed the opinion that 

 a diminution in the food-supply is the primary cause of the impulse, 

 and that individuals can be prevented from conjugating by increas- 

 ing the supply of food when the tendency first makes its appearance. 



According to the researches of Maupas the epidemic of conjugation in 

 Stylonychia pustulata reaches its height after 175 fissions. This author 

 also states that conjugation can be prevented by a suitable increase in 

 the food supply, and that senile decay and death occur after 316 fissions. 



