life which has culminated in man. This is bilateral 

 symmetry. It came as a consequence of the devel- 

 opment of the flatworm's creeping habits. But an- 

 other secondary trace of their result on the animal, 

 and one perhaps equally important, was wherein 

 its early efforts to creep led to the differentiation 

 of the fore from the rear. 



Although this flatworm is hermaphroditic, it is 

 quite certain that it can not fertilize its own ova. 

 For fertilization, it is necessary that sexual union 

 take place between two separate individuals. The 

 eggs are minute white spherules and are spawned 

 throughout the summer months, but instead of 

 being strewn broadcast in the water, as is the case 

 with Nereis, they are attached in closely aggre- 

 gated chain-like rows to stones, dead shells, and 

 other submerged objects. And here again is found 

 the beginning of an important factor which is re- 

 tained even by human kind; however, it is a factor 

 of function rather than of form. This factor is 

 found in the female organs; for the flatworm in- 

 variably comes by its clutches of eggs according 

 to the lunar cycle; that is to say, ovarian maturi- 

 ties occur a month apart. 



[i 7 6] 



