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- 
ees 
Fia. 96.—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 im 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 
