We have now traced hastily the eour: 

 into the sexes, but the question " what 



Starting with an amoeboid cell let us see what changes envi- 

 ronment might bring about in this direction. We have already 

 seen that nourishment evidently has considerable to do in the 

 determination of sex. Now the physiological conditions in 

 reference to nourishment to which a cell may be subjected are 

 evidently three: preponderating anabolism. preponderating 

 katabolism or a medium between these when katabolism and 

 anabolism are equal. Suppose an amoeboid cellis subject to a 

 preponderance of anabolism over katabolism the result would 

 naturally be, increase in size, accompanied by a growing regu- 

 larity of outline, increase in reserve food material and decreased 

 mobility. The result is surely plain, we would have differen- 

 tiated an ovum or egg cell. On the other hand subject the 

 amoeboid cell to preponderant katabolism, and we would as 

 reasonably expect a decrease in size and in reserve materials 

 accompanied by increased activity and the development ot 

 organs to aid in more rapid motion through the surrounding 

 medium. In short in this manner we reach intelligibly the 

 differentiation of sperm and ovum, antherozoid and oosphere 

 (fig. 60, and explanations). 



In certain of the Red Seaweeds we appear to have the curi- 

 ous and unparalleled occurence of two sexual acts in the life 

 cycle of the plant, and the manner in which it is lead up to by 

 transitional forms is very suggestive. The female reproductive 

 organs which are borne on the same plant as the antheridia or 

 on different ones consists usually of a group of cells, the pro- 

 carpium, from one of which the egg cell proper, a long contin- 

 uous closed tube, the trichogyne, grows out. In fertilization 

 the spermatia are wafted about in the water until they come 

 in contact with the trichogyne to which they adhere. The 

 walls at the point of contact are absorbed, allowing the nucleus 

 of the spermatia to pass over into the trichogyne and thus 

 down to the egg cell, where it unites with the female pronu- 



