SEXUAL EEPEODUCTION. 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 amass, 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 



Fig. 95. — Zygospore of Mucor pkycomyces. 



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 



