THE NUCLEI OF UROLEPTUS MOBILIS 355 



7. The second maturation spindles are usually 2 in number. 

 Each contains 8 chromosomes arranged in 4 pairs. Division 

 separates the members of each pair, resulting in reduction in 

 chromosomes from 8 to 4 (p. 316). 



8. All four products of the second division may undergo the 

 third division; or one, or two, may degenerate. The functional 

 pronuclei are always derived from the division of one of these 4, 

 the remainder degenerate (p. 319). The spindles are character- 

 ized by 4 chromosomes in the metaphase and anaphase stages, 

 and by long connecting strands in telophase stages (p. 321). 

 The pronuclei are not differentiated in size or shape ; the wander- 

 ing pronucleus is accompanied by a granular "^ attraction sphere' 

 of cytoplasmic origin (p. 323). 



9. Fusion of pronuclei begins while in the vesicular state; be- 

 fore fusion is complete the pronuclei assume a spindle form which 

 becomes the first division spindle with 8 chromosomes (p. 326). 



10. The first two nuclei divide again; one gives rise to the 

 functional micronuclei, the other to one micronucleus which de- 

 generates and to one which enlarges to form the new macronu- 

 cleus (p. 326). The conjugants separate at this stage. 



11. The new nuclear apparatus is formed by 3 divisions of the 

 new macronucleus and two of the micronuclei during the first 6 

 days subsequent to conjugation and the first division of the ex- 

 conjugant occurs on or about the sixth day. 



Columbia University 

 May. 1918 



THE JOCRNAI- Of EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 3 



