294 The American Naturalist. [April, 



coll which iv}. resents the ooblastema cell which by its further 

 growth gives rise to the spore complex (fig. 22). 



In other cases (Gloeosiphonia) when the contents of the 

 ooblastema filaments flow into the auxiliary cell, the nuclei 

 unite, the fusion or conjugation being thus complete. In this 

 case the auxiliary cell .-emirates off as an individual cell ami 

 gives rise to a lateral cell which becomes the centre of a spore 

 complex (fig. 23). . 



In the above case where the nuclei unite and where the 

 conjugation gives an impulse to further development in the 

 auxiliary cell, which otherwise would have remained quies- 

 cent, we have a case fulfilling all the requirements of a 

 true sexual act, — true fecundation, and there seems to be no 

 other way to consider this, than that here we have in the life 

 cycle of the plant, two entirely different sexual acts, one following 

 the other. We are surprised at this unprecedented phenomenon 

 but we can not predicate why it should not occur. The reason 

 for it we may assign to natural selection and development 

 along natural lines. (1) The spores develop at the ends of 

 filaments grown out from the egg cell. (2) The filaments thus 

 formed begin to attach themselves to cells of the branch for 

 nourishment. (3) We find special cells developed which the 

 ooblastema filament finds and unites with in one sense but 

 giving no nuclear union. (4) The ooblastema strikes a 

 specialized cell with which it unites nuclei and protoplasm, 

 the conjugation being complete and the further development 

 from this auxiliary cell. May we not here in the development 

 of the second sexual act of the Red Seaweeds derive a hint as 

 to the physiological meaning of fecundation. 



We start in a union for nutrition. We end with conjugation. 



FECUNDATION IN ANIMALS. 



Character of Ovum.— The animal egg or ovum presents all 

 the characteristics of a normal somatic cell. The rather large 

 nucleus is situated approximately in the centre of the cell, 

 surrounded by abundant protoplasm. The abundant chroma- 

 tin of the nucleus is arranged as in other cells in the form of a 

 tangled coil like a disordered ball of twine. It is thought by 



