SEXUAL REPRODUCTION, 165 
over one towards the other until their tops touch like a vice, 
each limb of which rapidly increases in size. Each of these 
arcuate, clavate cells has now a portion of its extremity isolated 
by a partition, by means of which a new hemispherical cell is 
formed at the end of each thread at its point of junction with 
the opposed thread. These cells become afterwards cylindrical 
by pressure, the protoplasm is aggregated into a mass, the double 
membrane at the point of first contact is absorbed, and the two 
confluent masses of protoplasm form a zygospore invested with 
a tubercular coat and enveloped by the primary wall of the two 
Fia. 95.—Zygospore of Mucor phycomyces. 
conjugating cells. During this formation of the zygospore, the 
two arched cells whence the zygospore originated develop a 
series of dichotomous processes in close proximity to the walls 
which separate them from the zygospore. These processes 
appear at first on one of the arcuate cells in successive order. 
The first makes its appearance above upon the convex side; the 
succeeding ones to the right and left in descending order; the 
last is in the concavity beneath. It is only after the development 
of this that the first process appears on the opposite cell, which is 
followed by others in the same order. These dichotomous pro- 
cesses are nothing more than branches developed from the arcuate, 
or mother cells. During all these changes, while the zygospore 
