1 86 THE EVOLUTION OF MAN. 



Eighth Stage: Monorhina Series (Fig. 190; PI. XI. Fig. 16). 



The ancestors of man are jaw-less skulled animals (resembling the 

 developed Myxinoides and Petromyzontes) . The number of the metamera is 

 increasing. The head is becoming more distinctly differentiated from the 

 trunk. The anterior end of the medullary tube swells into a bladder-like 

 structure and forms the brain, which is soon differentiated into five brain- 

 bladders. At the sides of these appear the three higher organs of sense. 

 The heart is divided into auricle and ventricle. The jaws, limbs, and 

 swimming-bladder are still wanting. 



Ninth Stage : Ichthyoda Series (Figs. 191, 192; PI. XII. and XIII.). 



The ancestors of man are fish-like skulled animals : first, Primitive 

 Fishes (Selachii), then mud-fishes (Pipneusiu), then gilled Batrachians (Sozura). 

 The ancestors belonging to this Ichthyoda stage develop two pairs of limbs: 

 a pair of anterior limbs (pectoral fins) and a pair of posterior limbs (ventral 

 fins). The gill-arches are formed between the gill-openings, and from them 

 are formed the first pair of jaw-arches (upper and lower jaws). The 

 swimming-bladder (lungs), liver, and pancreas grow from the intestinal 

 canal. 



Tenth Stage : Amniota Series (Figs. 195-208 ; PI. XIV.). 



The ancestors of man are amnion-animals or gill-less vertebrates : first, 

 Primitive amniota (Protamnia), then Primitive mammals (Mohotrema); next, 

 Pouched animals (Marsupialia) : then Semi-apes (Prosimice), and, lastly, 

 Apes (Simice). The ape-ancestors of man are first tailed Catarhini, then 

 tail-less Catarhini (Antliropoides), then speechless Ape-men (Alali), and at 

 last genuine, speaking men. The ancestors belonging to this amnionate 

 series develop an amnion and allantois, and gradually acquire the mam- 

 malian structure, and at last the specific human form. 



