MAtJPAS*S RESEARCHES ON OILIATE INPUSORIANS. 603 



conjugation a pair of Ciliata approach and adhere, fusing more 

 or less completely by their oral surfaces, and then separate 

 after a time : it has been long known that in this process 

 the nuclear apparatus undergoes a complete reconstruction. 

 What the nature of this reconstruction is, Maupas has now 

 revealed. 



The process of conjugation is divided by the author into 

 the eight following stages. In A the micronucleus enlarges 

 greatly. In B, C, D it undergoes successive bipartitions. Two 

 sister nuclei of the third bipartition (stage D) are specialised 

 as "pronuclei:" the one of these migrates into the other 

 gamete to fuse with the stationary pronucleus there ; and this 

 process constitutes stage E. The " copulation-nucleus " so 

 formed undergoes two fresh bipartitions in stages F and G. 

 In stage H the nuclear apparatus is reconstituted and the first 

 bipartition takes place. 



In the five stages B, C, D, F, G, involving nuclear division, 

 we can distinguish the following substages or phases: (1) 

 Spirema, the nucleus shows a reticulation; (2) aster, the 

 chromatin forms distinct thickish rods, extending the greater 

 part of the fusiform nucleus, its poles being occupied by fine 

 achromatic filaments; (3) equatorial plate; (4) diaster, the 

 chromatin rods are in two groups united by achromatin fila- 

 ments ; (5) dispirema, the two chromatin groups are more 

 distant, and contorted, and united by achromatin filaments 

 which are strangulated in the middle, or contained in a dilated 

 connective tube (boyau), which is soon absorbed into the 

 ambient cytoplasm. Thus Gg would indicate the aster stage 

 of the second bipartition of the copulation-nucleus. 



In stage A we may also distinguish four substages: (1) the 

 micronucleus unchanged ; (2) swelling without much change 

 of form ; (3) further swelling with changes of form charac- 

 teristic of the species; (4) the micronucleus condenses and 

 shrinks by way of preparation for its first bipartition in 

 stage B. 



Stage E is also divided into phases: E^, the male pronucleus 

 approaches the point of exchange; E3, it passes into the fellow- 



