( 346 } 



EXPLANATION OF PLATE L— (Fkoktispiece ) 



Development of the Face. 



The twelve figui-cs in Plate I. represent the faces of fonr different 

 Mammals in three distinct stages of individual evolution: Mi-Miii that of 

 Man, Bi-Brii of the Bat, Ci-Ciii of the Cat, Si-Siii of the Sheep. The 

 three different stages of evolution have been chosen to correspond as far as 

 possible ; they have been reduced to about the same size, and are seen from 

 in front. In all the figures the letters indicate the same : a, eye ; v, fore- 

 brain ; m, mid-brain ; s, frontal process ; h, nose-roof ; o, upper jaw process 

 (of the first gill-arch) ; u, lower jaw process (of the first gill-arch) ; h, 

 second gill-arch; d, third gill-arch; r, fourth gill-arch; g, ear-fissure 

 (remains of the front gill-opening) ; z, tongue. (Cf. Plates VI. and VII., 

 Figs. 232-236, p. 243 ; also Figs. 123, 124, vol. i. p. 370.) 



TABLE XXXVII. 



Systematic Survey of the most Important Periods in thb 

 Phylogeny of the Human Intestinal System. 



I. First Period: Intestine of Gastroea (Figs. 274-277; Plate V. Figs. 9, 10). 

 The whole intestinal sj^stem is a simple pouch (primitive intestine), the 

 simple cavity of which has one orifice (the primitive mouth). 



II. Second Period : Intestine of the Scolecida (Plate V. Fig. 11). 



The simple intestinal tube widens in the middle into the stomach, and 

 vcquires, at the end opposite to the primitive mouth, a second opening 

 (primitive anus) ; as in the lower Worms. 



III. Third Period: Intestine nf Chorda Animals (Fig. 281; Plate V. Fig. 12). 



The intestinal tube differentiates into two main sections — the respiratory 

 hitestine with gill-openings (gill-intestine) in front, the digestive intestine 

 with stomach-cavity (stomach-intestine) behind ; as in Ascidia. 



