PHENOMENA ACCOMPANYING FERTILIZATION 307 



Woodruff and Erdmann (1914) called endomixis (see p. 317). 

 Experimental evidence leading to definite conclusions has not yet 

 been advanced. Calkins (1921) made an attempt in this direction 

 by cutting conjugating pairs of Uroleptus mobilis in such a way that 

 the two migrating pronuclei were removed while the two individ- 

 uals, now separated, possessed only the stationary pronuclei (Fig. 

 155). These individuals were then followed in cultures, the process 

 of reorganization was completed, the cells regenerated perfectly, 

 and in successful issues, normal rejuvenescence and a typical life 

 history resulted. The crucial point so far as the present matter 

 is concerned was not determined, viz., from what elements were the 

 new macro- and micronuclei derived? Did the stationary pro- 

 nucleus in its "unbalanced" condition give rise to the new nuclear 

 elements as it would have done were it an amphinucleus? Was 

 there a fusion prior to the degeneration of other pronuclei of the 

 stationary pronucleus with one of the "male" pronuclei of which 

 there may be as many as four in each conjugant? Or did the sta- 

 tionary pronucleus degenerate, its place being taken by one of the 

 other pairs of pronuclei? Some evidence that the last alternative 

 was the case is afforded by the fact that the conjugating pairs if cut 

 apart at an early period in conjugation may not undergo the third 

 division, some one of the products of the second division acting as 

 an amphinucleus, thus realizing the condition during "endomixis." 

 See also, in this connection, the merotomy experiments of Ilowaisky 

 (1926) on Stylonychia mytilus and Paramecium caudatum conjugants. 

 (6) Gametic Meiosis (Wilson, 1925). — In the preceding section 

 instances of meiotic divisions subsequent to cell fusion were inter- 

 preted as due to stimuli mutually imparted to the conjugating 

 individuals. For this the protoplasm must be in a mature condition, 

 that is, with an organization considerably modified from that of the 

 young or immature organisms. In a later section evidence will be 

 given which indicates that under proper conditions the stage is all 

 set for a similar all or none series of phenomena without, however, the 

 stimulus of contact (see p. 317, endomixis). An analogous condi- 

 tion termed here gametic meiosis if accompanied by subsequent cell 

 fusion of gametes, is characteristic of the majority of Protozoa 

 in which fertilization is accomplished by the fusion of cells. Unfor- 

 tunately the history of the chromosomes is known in but few cases 

 but there is scarcely a paper on the fertilization of Protozoa that 

 does not describe two rapidly-following divisions of the nuclei 

 prior to fusion, and these are called maturation divisions, and the 

 resulting nuclei "reduction nuclei." In Actinosphaerium eichhornii 

 according to Hertwig (1898) the first evidence of the process is 

 encystment of the adult organism and excretion of waste matters 

 contained in the protoplasm. The nuclei are reduced in number to 

 from 5 to 10 per cent of the original number by fusion and absorption 



