240 



COMPARATIVE ANATOMY 



of division may again divide, giving rise to four microgametes, 

 but a single binary division is the rule.* 



The microgametes when set free from the parent stalk swim 

 through the water. Conjugation begins towards the hour of 



Stages in the conjugation of I'orticella monilata ; mac, macrogamete ; mic, micro- 

 gamete. M, fragmented meganucleus of the macrogamete. M', fragmented 

 meganucleus of the microgamete. W, water accumulated below the peristome 

 of the macrogamete ; in, micronucleusof the macrogamete ; t/i , micronucleusof the 

 microgamete; en, combination nucleus. For further description see text. (After 

 Maupas.) 



daybreak and lasts from thirteen to fourteen hours. A micro- 

 gamete coming into contact with a fixed macrogamete attaches 

 itself by its posterior end to the hinder region of the body of 

 the latter, and immediately becomes intimately fused with it. 

 So long as it is swimming about freely the microgamete has a 



* It has been so commonly stated that Vorticella gives rise by three 

 successive binary divisions to eight microgametes that it is well to insist 

 on the fact that Maupas has found that the microgametes are formed by 

 equal binary division in V . monilata, V . putrina, and V . nebulifera ; by 

 unequal binary division in V . microstoma ; and only by repeated binary 

 division in the case of Carchesinm polypimnii. 



