SEXUAL REPRODUCTION. 167 



there is collected an abundance of protoplasm, and when they 

 have attained a certain development the largest extremity of 

 each is isolated by a septum from the clavule, which thus becomes 

 the support or suspender of the copulative cell. The two conju- 



Jkss 



FIG. 93. Zygospore of Rhizopus in differeut stages. (De Bary.) 



gated cells of the fusiform body are generally unequal ; the one 

 is a cylinder as long as it is broad, the other is disciform, and 

 its length is only equal to half its breadth. The primitive mem- 

 brane of the clavule forms between the copulative cells a solid 

 partition of two membranes, but soon after the cells have become 

 defined the medial partition becomes pierced in the centre, and 

 then soon entirely disappears, so that the two twin cells are 

 confounded in one single zygospore, which is due to the union 

 of two more or less similar utricles. After its formation the 

 zygospore still increases considerably in size, and acquires a 

 diameter of more than one-fifth of a millimetre. Its form is 

 generally spherical, and flattened on the faces which are united 

 to the suspenders, or it resembles a slightly elongated cask. 

 The membrane thickens considerably, and consists at the time 

 of maturity of two superposed integuments ; the exterior or 

 epispore is solid, of a dark blackish-blue colour, smooth on the 

 plane faces in contact with the suspenders, but covered every- 

 where else with thick warts, which are hollow beneath. The 

 endospore is thick and composed of several layers, colourless, 

 and covered with warts, which correspond and fit into those of 

 the epispore. The contents of the zygospore are a coarsely 



