Interpretation of Facts 



159 



is six thousand. This means that Paramoecia do not die, though they 

 can be killed, e.g., by boiling, by immersion in acids, and in other ways. 

 It means further, that every Paramoecium in existence is actually a part 

 of all its ancestors; or more accurately, it is its ancestors, for these 

 ancestors have never ceased to be. This must be true, because each, 

 ancestor merely divided into two offspring, the offspring being in reality 



the parent itself. 

 This is different 

 from a parent giving 

 birth to an offspring 

 and then dying. 



It is an estab- 

 lished biological fact 

 that no living cell 

 can come from any- 

 thing but a previous 

 living cell. No or- 

 ganism or living 

 thing can come into 

 existence except 

 from some previous- 

 ly existing living 

 parent form. 



Now, if suf- 

 ficient food is given 

 Paramoecia, they 

 keep on dividing sev- 

 eral hundred times; 

 but, if they are with 

 others of their kind, 

 an interesting event takes place. Two of the animals will swim around, 

 finally attaching themselves to each other lengthwise, while the wall of 

 each animal which is in contact with its mate seems to disappear, the 

 two animals becoming almost, but not quite, one. 



The smaller colorable spot in each animal now begins to divide into 

 two parts as shown in Fig. 81. These parts again divide, making four 

 pieces of each nucleus. Three of these pieces disappear (probably are 

 dissolved in the body substance). The one remaining piece then divides 

 into two pieces, one of which remains more or less stationary, while the 

 other (often partially connected with the first) moves toward the mid- 

 line of the two connected animals to meet with a similar movable piece 

 of stainable matter from the attached individual. The two pieces of 

 movable, stainable matter become one for a short period, seemingly 

 exchanging some of their substance. Then they again separate and form 

 a nucleus like the one from which they sprang. 



The animals themselves now separate, and each divides into two 

 new animals. These again divide, such division continuing as already 



Fig. 81. 

 Stages in the conjugation of Paramoecium caudatum. A, Stage A, 

 the micronucleus in each gamete preparing for division. B, Stage B, 

 the daughter nuclei in each gamete dividing. C, Four micronuclei in 

 each gamete. D, three of the four micronuclei are disintegrating; the 

 surviving nucleus in each gamete has divided to form cf, the male, 

 and 9, the female pronucleus. F, The male pronuclei crossing over. 

 F, Conjugation effected; separation of the gametes and division of 

 the combination nucleus. (After Maupas.) 



