Igor] GAMETOGENESIS AND FERTILIZATION IN ALBUGO 165 
naturally suggest a possible derivation of the two former groups 
through the latter. However, as Schréter (1893) has remarked, 
* Durch das vollstandige Fehlen von Schwarmsporenbildung, das 
oft rein fadige Mycel, die fast nur an der Luft terminal gebildeten 
Sporen entfernen sich die M. immer weiter von den Algen;” 
and it is difficult to regard the Mucorineae ancestral to these 
other Phycomycetes. The manner in which the Mucorineae 
may have arisen from ancestral algae has been discussed by 
Davis (1900, p. 308), who has indicated the similarity between 
the coenogametes of Mucorineae and those of A. Bit. Not- 
withstanding this similarity it does not seem advisable to regard 
the Mucorineae as a line productive of such forms as the Per- 
onosporaceae and Saprolegniaceae for the reasons expressed 
above. The similarity of the vegetative body, however, is 
sufficient to indicate the possibility, even probability, that the 
Siphoneae, Mucorineae, Peronosporaceae, and Saprolegniaceae 
constitute three distinct lines of development from a common 
parent stock. 
Since transition stages in the evolution of these groups are 
not known, the phylogeny of the coenogamete is little more 
than a matter for speculation. Two modes of origin are con- 
ceivable; either the coenogamete arose from a gametangium 
producing numerous gametes through the failure of the gametes 
to separate and become completely individualized; or it may be 
regarded as a structure, originally multinucleate, which arose 
and attained sexual differentiation through a line of ancestry 
composed of multinucleate zoospores. 
According to the first view the coenogamete is ‘morpholog- 
ically a gametangium or physiologically a compound gamete. 
Each nucleus is the nucleus of a gamete. According to the latter 
view the coenogamete itself is homologous with a gamete, being 
a multinucleate gamete. Arguments in support of either view 
must be based upon such fragmentary evidence as is afforded by 
the present existing species (which may be made to stand for 
Stages in phylogeny), or the partial repetition of phylogeny 
through ontogeny. Unfortunately, very little evidence can be 
