1 86 THE EVOLUTION OF MAN. 



Eighth Stage: Monorhina Series (Fig. 190; PI. XI. Pig. 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 (Dipneusta) ,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 (Monotrema) ; 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 (Anthropoides), 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 lost the specific human form* 



