22 • MEDICAL MYCOLOGY 



the mother cells gametangia. The copulation of two gametes of this type is 

 called merogamy. If the gametes appear wholly of the same size and shape, 

 the copulation is isogamous; if the gametes are differentiated, their copulation 

 is heterogamous (anisogamous). When the female gamete is a large and non- 

 motile egg and the male gamete is a small and motile sperm, their copulation 

 is oogamous, a condition confined to primitive fungi, although present in most 

 higher animals and primitive plant phyla. 



The more advanced fungi show various stages in the degeneration of 

 merogamy. At a comparatively low stage, the differentiation of gametes is 

 suppressed and the contents of the gametangia remain polyenergid. Thus 

 the original copulation of gametes disappears, being replaced by many sec- 

 ondary processes which compensate for the loss of the original merogamy. 

 All these secondary processes are classified as deuterogamy. The higher algae 

 and flowering plants have also developed these processes, while the primitive 

 merogamy has persisted through the highest vertebrates. 



In deuterogamy, the gametangia assume the function of their daughter 

 cells, the gametes, and their coenocytic content fuses without further differ- 

 entiation. The sexual act occurs between two sexual organs instead of between 

 two sexual cells and sexual attraction passes from the latter to the former. 

 This type of copulation is called gametangial. It assumes close contact be- 

 tween two gametangia and has a biologically obvious consequence that one 

 gametangium can fertilize only one other which must be located nearby ; it 

 has the advantage that the fusion of gametes is no longer fortuitous, since the 

 gametangia provide that their nuclei can come into contact and fuse. Thus 

 gametangial copulation is an efficient type, since most of the nuclei of both 

 gametangia succeed in their activity with an increase in the number of zygote 

 nuclei. The fate of the gametangium hangs upon the occurrence or nonoc- 

 currence of a single sexual act, from which results one single, very strong, 

 coenocytic zygote instead of many smaller unicellular zygotes. Also a single 

 mature gametangium no longer depends on a definite medium (e.g., water) 

 for the copulation of its gametes, a condition which has facilitated the transi- 

 tion from water to land habitats and to parasitism. Whether gametangia are 

 borne on specialized branches or whether hyphal branches as a whole complete 

 the act of fertilization, they are called copulation branches. When sexual 

 dimorphism is present, the male is called an antheridium and the female an 

 ascogonium. 



Among the higher Ascomycetes, the fundaments of the antheridium are 

 gradually reduced, whereby cross-fertilization generally ceases and is replaced 

 by self-fertilization, i.e., a new group of deuterogamous processes, between 

 daughter cells of the same mother cell or between nuclei of the same cell, 

 which are included in the term automixis. 



Automixis is represented in fungi by two forms : parthenogamy and 

 autogamy. Parthenogamy is fertilization which occurs between two female 

 cells, i.e., in fungi usually between two cells of the ascogonium. In some 

 groups this parthenogamic fusion of two specialized cells is replaced by the 



