WHAT IS AX OKGAAISM ? 



171 



In this case the generation is sexual, but JicrmapJiroditc, 

 and the product of generation is set free after being developed 

 sufficiently to carry on independently the functions of life. 



The other mode of gamogenesis is dia'cious (V), in which 

 the differentiation of sex has proceeded so far as to affect 

 individual life, and to require the co-operation of two differ- 

 ent individuals for the accomplishment of the function. This 

 is the more frequent mode of generation in the animal king- 

 dom. It may be represented diagrammatically by Fig. 47. 



The Several Stages of Development in the Higher Organisms. — In 

 this series there are several stages of development which it is 



Fig. 48. — Segmentation of the ovum. A, B, C, various stages of segmentation. Z>, blastula. 



(After McINIurrich.) 



important to note. There is, first, the stage of sex differentia- 

 tion in the individual, the one being called male, the other 

 female. This appears early in the life of the individual, but 

 in its earliest stages there appears no discernible difference of 

 form in the organs of the two sexes. 



Second. This distinction is carried on independently in 

 the growth and development of each kind of individual ; organs 

 are specialized and differently formed, and finally result in the 

 production of specialized cells, called in the one case 

 Spcrmulc iSpcrniatozoaii), and Ovule {Ovuui) in the other. 



Third. The conjunction of the spcrmulc and ovule, formed 



