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TABLE XLIII. 



SYSTEMATIC SOKVEI OF THE MOST IMPORTANT PERIODS IN THE PHYLOOBX* 

 OF THE URINARY AND SEXUAL ORGANS OF MAN. W 



XLIII. A. First main division : the sexual organs (G) and the urinary 

 organs (U) are distinct. (The sexual or genital system (G) and tht 

 excretory or urinary system act independently of each other.) 



I. Firs* Period : Genitals and Kidneys of Gastrceads. 



G. Single, scattered cells of the entodenn change into egg-cells ; single, 

 scattered cells of the exoderm into sperm-cells. 



U. Special urinary organs are as yet wholly waating. Secretion is 

 performed by the cells of the exoderm. 



IL Second Period : Genitals and Kidneys of Primitive Worms. 



G. The egg-cells of the entodenn gather into groups (ovary -plates) ; as 

 do the sperm-cells of the exoderm (testis -plates). 



U. A pair of simple pouch-like skin-glands (products of the skin-sensory 

 layer) develop into extremely simple kidney-canals (excretory organs of the 

 Flat-worms, Platelminthes). 



III. Third Period: Genitals and Kidneys of Scolecida. 



G. After the differentiation of the four secondary germ-layers is coin, 

 plete, the egg-cells pass from the skin-sensory layer into the skin-fibrons 

 layer ; the sperm-cells also pass from the intestinal-glandular layer into the 

 intestinal-fibrous layer. 



U. After the formation of the ccelom is completed, the blind inner ends 

 of the two kidney-canals (or "primitive kidney ducts") open into the body- 

 cavity (cceloma). 



IV. Fourth Period : Genitals and Kidneys of Chordonia. 



G. The groups of egg-cells (ovarial plates) and the groups of sperm-cells 

 (testes-plates) meet at the boundary between the endocoelar (the visceral 

 intestinal-fibrous layer of the coelom-epithelinm) and the exoccelar (tho 

 parietal skin-fibrous layer of the coelom-epithelium), so as to form the 

 hermaphrodite glands. 



U. The primitive kidney ducts differentiate into an excretory and a 

 glandular part. 



V. Fifth Period : Genitals and Kidneys of A crania. 

 O. The sexes become distinct. In the female, only the ovary is de- 

 veloped ; in the male, only the testes. 



U. The primitive kidney ducts remain simple (atrophied in Amphioxus). 



