UNION OF FREE-LIVING CELLS 289 



readily coalesce ; on the other hand, homoiogenous pseudopods which contact 

 each other shatter into small particles or droplets ; but this does not apply to 

 the main bodies of these organisms, which are more resistant. Shattering 

 apparently represents a characteristic homoio-reaction and it is lacking if 

 heterogenous individuals come in contact. On the other hand, heterogenous 

 protoplasms do not fuse with each other as readily as autogenous ones. The 

 heterogenous reaction resembles, in certain respects, that noted towards 

 foreign material ; however, these heterogenous particles, in contrast to food- 

 stuffs, are not incorporated into the main body of the protozoa. 



The dependence of the reactions of individual protozoa on relationship is 

 evident also in the subsequent investigations of Reynolds. He started with a 

 single individual in Arcella, which, in the course of time, underwent fissions, 

 and this process was continued through several generations ; a comparison 

 was then made between the behavior of the individuals towards each other 

 in the later and in the earlier generations of such cultures. Reynolds found 

 that although all these individuals were originally derived from a single cell, 

 after some time they began to react towards each other as if they were ho- 

 moiogenous organisms, and shattering occurred if two such individuals be- 

 longing to later generations met. Such a change from an autogenous into a 

 homoiogenous reaction took place after about twenty-two consecutive fissions, 

 even in cells which had been kept under the same environmental conditions, in 

 the same culture fluid. However, if individuals developing through fission 

 of the same protozoon were separated from each other at once and kept in 

 different culture fluids, representing a somewhat different chemical environ- 

 ment, then the homoio-reaction was attained sooner. 



But Reynolds was also able to obtain the reverse transformation. For this 

 purpose he proceeded in the following way : after he had changed syngenesious 

 individuals into homoiogenous ones, he succeeded by means of daily ex- 

 change of the culture fluid — placing Arcella A into the fluid in which Arcella 

 B had lived — in transforming the homoiogenous reaction back into a syn- 

 genesious or an autogenous one. If such individuals were kept together in the 

 same culture dish, the return to the autogenous reaction could be obtained even 

 sooner. It appears then, that we have, under these conditions, not to deal with 

 rigid, mutation-like changes in the protoplasm, but with changes of a more 

 labile nature, which occur in response to environmental factors and that these 

 changes are reversible. This holds good provided the genetic constitutions of 

 the individuals were closely related to each other from the beginning, as is 

 the case if the organisms are derived through fission from a single individual. 



Such experiments suggest that into the culture fluid substances diffuse 

 which are characteristic of the individual organism and with which presum- 

 ably their surface layers become impregnated. These substances would then 

 be responsible for the type of reactions that follow the meeting of two indi- 

 viduals, or at least be one of the factors involved. It must further be assumed 

 that the protoplasm of these organisms is readily modifiable and that in the 

 course of continued fissions a change gradually takes place, leading to a cor- 

 responding modification in the character of the substances which they give 



