290 The American Naturalist. [April, 



tion has been carried further, the female having become wholly 

 ineap.ihle of independent motion, and the antherozooids have 

 been gradually decreasing in comparative size. Here we have 

 reached as high a development of fecundation as is probably 

 found in the vegetable kingdom. (The stages in this develop- 

 ment may be made clear by an examination of tig. 20, which 

 is a modification of an illustrativ.> diagram designed bvGeddes 

 and Thomson.) 



I trust I have now made clear to you how fecundation prob- 

 li'iy mi ioinated, or rather the course it likely pursued in its 

 gradual differentiation. Cell division, as we have seen, origi- 

 nated in almost a mechanical breaking apart of a mass of pro- 

 toplasm. Conjugation and fecundation we now see, probably 

 originated in the almost mechanical adhesion of the swarm 

 spores of the Acrasiex, followed by the mechanical fusion of 

 the swarm spores of My-conn/crt,*, uw\ gradually increasing in 

 complexity until there is complete fusion (conjugation), then a 

 fusion of elements differing in character. Which is fecunda- 



DIPFERENTIATION OF SEX. 



We may now direct our inquiry to the point in this evolu- 

 tion where sex becomes differentiated. In the conjugating 

 swarm spores of the Slime Molds there seems to be no point 

 where we can detect indications of a difference in the uniting 

 individuals. So far as known there is no differentiation into 

 male and female. 



In Uothrix (fig, 17) we begin to get a differentiation. In 

 the conjugating microzoospores or planogametes (so called 

 because of their similar character), it has been observed that 

 planogametes produced in the same organ or gametangium 

 will not coalesce with each other, but coalesce with planoga- 

 metes from other gametangia. Here then, where the micro- 

 scope fails to reveal any difference in the conjugating cells we 

 nevertheless know from this fact that there must be some dif- 

 ference. 



Edocarpus siliculosus, one of the brown seaweeds, from the 

 observations of Berthold, illustrates a rather different feature, 

 by which we determine that the planogametes are really male 



