46 FECUNDATION ; NON-MOTILE ISOGAMETES. 
the others being disorganized; and in the desmids only two out of the 
four in the germination of the zygote develop into perfect cells. 
It is not known whether the reduction in the number of chromo- 
somes, if a reduction actually occurs in either desmids or diatoms, is 
in any way associated with the nuclear divisions in question, as has 
been assumed by some authors (see Wilson, ‘‘ The Cell,” p. 198) ; 
consequently, in the light of our present knowledge, it cannot be said 
with any certainty that these nuclear divisions represent a preparation 
for the sexual act, that in the diatoms taking place just before fecun- 
dation while in the desmids it occurs at the beginning of an ontoge- 
netic development. 
BASIDIOBOLUS. 
A sexual process similar to that in the Conjugate@ is found in 
Basidiobolus, one of the Phycomycetes. I have selected Basidzo- 
Fig. 24.—Fusion of the sexual nuclei in Rhefa- 
lodia gibba.—(After Klebahn.) 
I, the two young zygotes or auxospores have elon- 
gated and begun to assume form of adult; sexual 
nuclei now in contact. 
J, middle portion of two auxospores, each with a 
» fusion nucleus. 
bolus ranarum because of its close re- 
semblance to certain Mesocarpacee, 
especially Mougeotza, both in structure 
(the cells possess only one nucleus) and 
in the sexual process, and because the development of the sexual 
organs and the fusion of the gametes are well known in detail. Sex- 
uality in this genus has recently been subjected to a critical study by 
Fairchild (’97), whose results form the basis of the following account. 
Two neighboring cells of a filament send out near the transverse 
wall a beak-like protuberance, into which the nuclei of the respective 
cells pass (Fig. 25, A). 
The nucleus in each of the protuberances now undergoes a karyo- 
kinetic division, which is followed by the formation of a transverse 
