346 GARY N. CALKINS 



ical relations are fairly uniform, two spindles in the second 

 maturation division being the rule. There are, however, some 

 exceptions. Thus in Paramecium bursaria, according to Ham- 

 burger ('04), one of the nuclei formed by the first maturation divi- 

 sion degenerates without forming a spindle, so that only one 

 nucleus undergoes the second maturation division. A second 

 exception is found in Euplotes patella and in all vorticellidae 

 examined up to the present time. Here the micronucleus under- 

 goes one preliminary mitosis prior to the first maturation divi- 

 sion (p. 338). The resulting two nuclei then undergo the first 

 maturation division and the four resulting nuclei form eight by 

 the second maturation division. In vorticellidae this unusual 

 division occurs only in the microgamete. The micronucleus of 

 the macrogametes, on the other hand, does not undergo a pre- 

 liminary divisipn and the usual history of uninucleate forms is 

 followed. 



In ciliates with two micronuclei, both undergo the first matu- 

 ration division. According to Prowazek ('99), the four resulting 

 nuclei in Stylonychia pustulata divide again, thus forming eight 

 products of the second division. According to Maupas ('88), 

 however, two of these first four nuclei of Stylonychia pustulata, 

 and of Onychodromus grandis as well, degenerate so that only 

 two nuclei divide in the second maturation division. 



In ciliettes with many micronuclei in the vegetative stage there 

 seems to be no general rule as to the number which undergo the 

 second maturation division, unless, indeed, it be variability. 

 Prandtl ('06) found a variable number in Didinium nasutum; 

 Prowazek, ('99) a large number in Bursaria truncatella, and I find 

 a variable number in Uroleptus mobilis. The usual number of 

 spindles in the second maturation division here is two, although 

 three are frequently found, while individuals with one or with four 

 have not been seen. 



d. The third division. The third, or pronuclei-forming divi- 

 sion, is a peculiarity apparently almost universal in the Infusoria. 

 The spindles are frequently heteropolar (Didinium, Paramecium), 

 and the telophase stage is often characterized by long connecting 

 strands of nuclear substances (Paramecium Blepharisma, Uro- 



