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TABLE XLIII. 



Ststkmatio BtmvBT of the most Important Periods ih thb Prtloobn) 

 OF THE Urinary and Sexual Organs of Man.^*' 



XLin. A. First main diTision : the BexuiU organs (G) and the arinary 

 organs (U) are distinct. (The seznal or genital system (G) and th« 

 excretory or urinary system act independently of each other.) 



I. First Period : OenitaU a/ad Kidneys of OastrcBads. 



Q. Single, scattered cells of the entoderm change into egg-oeHs ; single, 

 scattered cells of the exoderm into sperm-oells. 



U. Special arinary organs are as yet wholly waiting. Seoretrai i» 

 performed by the cells of the exoderm. 



IL Second Period : Genitals and Kidmeys of Primitive Worms, 



G. The egg-cells of the entoderm 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 

 Plat-worms, Platelminthes). 



III. Third Period : Genitals and Kidneys of Scotedda, *" 



Q. After the differentiation of the four secondary germ-layers is com. 

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

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

 intestinal -fibrous layer. 



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

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

 cavity (eoslotna). 



rV. Fourth Period : Genitals amd Kidm.eys of Chordonia. 



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

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

 intostinal-fibrous layer of the coelom-epithelium) and the exocoelar (the 

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

 hermaphrodite glands. 



T7. The primitive kidney ducts differentiate into an excretory and • 

 glandular pari. 



V. Fifth Period : Genitals a/nd Kidneys of Aerania. 



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

 raloped ; in the male, only the testes. 



XJ. The primitive kidney ducts remaan simple (atrophied in Atnphioausy 



