SEXUAL REACTIONS BETWEEN MUCORS. 89 



the sexual reaction is very strong it may become evident to 

 the naked eye by the formation of a distinct white line as is 

 shown in the adjoining photograph. 



Some few species in the hermaphroditic group are distinctly 

 heterogamic with a constant difference in size between the conju- 

 gating gametes. It seems reasonable to consider the larger 

 gamete female and the smaller male. Upon this basis, if a sexual 

 reaction could be established between these unequal gametes 

 and the ( + ) and ( ) races, the race reacting with the larger 

 female gamete must be considered male, while the race reacting 

 with the smaller male gamete must be considered female. This 

 was pointed out in 1906 ('066) and in a recent article ('136) it 

 has been shown in brief that sexual reactions have been induced 

 between unisexual races and heterogamic species. The conclusion 

 is reached that the ( ) race is to be considered male and the 

 (+) female. The present article will give the detailed results 

 which have formed the basis for this conclusion. 



HETEROGAMIC HERMAPHRODITES. 



Since inequality in the size of the gametes in heterogamic 

 species is used as the criterion of sex, it is essential that there 

 be no doubt as to the process of sexual reproduction in these 

 forms. With the exception of Syncephalis, which is difficult to 

 cultivate, the heterogamic forms at present known are Dicra- 

 nophora fulva and an undescribed American Dicranophora,. 

 neither of which are now in cultivation, Absidia spinosa, 

 Zygorhynchus heterogamus, Z. Moelleri and a number of forms 

 recently described (including Z. Vuillemini) which are perhaps 

 too closely allied to Z. Moelleri to be deserving of separate names. 



The writer in a recent publication ('i3#) has made a restudy 

 of the genus Zygorhynchus and attempted to correct certain 

 misinterpretations of zygospore formation which had been 

 advanced for this genus. Moreau ('12, '13) also, both before 

 and since the publication mentioned, has insisted upon the 

 correct interpretation. So far as concerns the formation and 

 union of unequal gametes, the process is essentially similar to 

 that in Absidia spinosa which is the heterogamic species most 

 extensively used in the tests discussed in the present paper. 



