( 346 ) 



EXPLANATION OF PLATE I.— (Frontispiece.) 

 Development op the Face. 



The twelve figures in Plate I. represent the faces of four different 

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

 Man, Bi-Biit 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 ; fc, nose-roof ; o, upper jaw process 

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

 Becond 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 j also Figs. 123, 124, vol. i. p. 370.) 



TABLE XXXVII. 



Systematic Survey of the most Important Periods in thb 

 Phylogeny op the Human Intestinal System. 



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

 The whole intestinal system 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 

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

 (primitive anus) ; as in the lower Worms. 



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

 The intestinal tube differentiates into two main sections — the respiratory 

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

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



