PHENOMENA ACCOMPANYING FERTILIZATION 291 



ditions. With Urolejptus mobilis conjugation and encystment tests 

 are made in exactly the same way and in some tests conjugating 

 pairs and encysted forms are present simultaneously. 



In the case of Uroleptus mobilis a mass culture of young indi- 

 viduals shows no tendency to agglomerate, the cells are distributed 

 more or less uniformly in the culture. In similar mass cultures of 

 individuals approaching maturity agglomeration in dense groups is 

 highly characteristic. Such cultures may show no conjugations, 

 but a mass culture made with the progeny of the same individuals 

 a week later will show not only the initial agglomerations but epi- 

 demics of conjugation as well (Calkins, 1919). 



This phenomenon of agglomerations indicates something of the 

 nature of an attraction that increases in intensity as the organisms 

 approach maturity and have a bearing on the problem of mating. 

 What is it that brings two gametes together or two apparently simi- 

 lar ciliates? There is some evidence .that the attraction is of a 

 chemiotactic nature as illustrated by the often quoted experiment 

 of Pfeiffer with malic acid and fern spermatozoids. Two citations 

 from Engelmann (1876) illustrate this phenomenon with ciliates 

 of the genus Vorticella: "The buds, at the beginning, swarmed 

 about with constant and considerable rapidity rotating the while on 

 their axes but moving more or less in a straight line through the 

 drop. This lasted from five to ten minutes or even longer without 

 any special occurrence. Then the scene suddenly changed. Hap- 

 pening in the vicinity of an attached Vorticella a bud quickly 

 changed its direction with a jerk and approached the larger form, 

 fluttering about it like a butterfly over a flower and gliding over its 

 surface here and there as though tasting. After this play, repeated 

 upon several individuals, had gone on for several minutes, the bud 

 finally became firmly attached." Again: "I observed another per- 

 formance still more remarkable. A free-swimming bud crossed the 

 path of a large YorticeUa which had become free from its stalk in the 

 usual manner and was roaming about with great activity. At the 

 instant of the meeting, there was no trace of a pause, the bud sud- 

 denly changed its direction and followed the Vorticella with great 

 rapidity. It developed into a regular chase which lasted about five 

 seconds during which time the bud remained about jj of a milli- 

 meter behind the Vorticella although it did not become attached 

 for it was lost by a sudden side movement of the larger form" 

 (Inc. cit., p. 583). Another illustration taken from the observa- 

 tions of Schaudinn (1900) on the mating of gametes of Eimeria 

 schubergi, suggests an action analogous to that of attraxin as 

 described by F. R. Lillie in sea-urchin eggs. During the matura- 

 tion of the macrogamete of Eimeria schubergi, the "karyosome" is 

 cast out of the nucleus, breaks into fragments and the fragments 

 are extruded from the cell, remaining, however, attached to the 



