" ARBOREAL MAN " 215 



This, however, tells us little about the " how " of the Therap- 

 sidian achievement. In a trice we are confronted by a " blend 

 of primitive reptilian and primitive mammalian characters," 

 by a type which apparently flourished exceedingly after the 

 manner of " dominant " races. Whence did the Therapsida 

 derive their dominance and power to support their bodies by the 

 limbs ? We shall not be far wrong in assuming that the source 

 was the symbiotic plant. The mammalian character is a monument 

 to partnership partnership so far as physiological and special 

 sexual arrangements are concerned and founded in turn upon 

 biological partnership, i.e., as between animal and plant. These 

 factors alone are certain ; all else is uncertain. What the particular 

 plants were with which the Therapsida or their ancestors lived 

 in partnership, is for Palaeontology to say. The discovery of 

 these Triassic plants, if not already made, should not prove 

 too difficult a feat to accomplish. 



If it had not been in the first place that the finer allurements 

 of the plant's products had appealed to the corresponding senses 

 of the Therapsida, they could scarcely have been abidingly and 

 successfully attracted to the branches of the trees. Nor, without 

 the vital pabulum there obtainable, would they have been able 

 to shoulder the burdens and sacrifices incumbent upon mammalian 

 life. The blend of good characters in the Therapsida, we may 

 confidently believe, was not due to a coincidence ; but it was 

 due to the prevalence of comparatively high forms of Symbiosis. 



The Therapsida, in approaching the mammalian status, were 

 not, we may assume, after the " graces of life." And if it be not 

 purely their " slow willing " that has produced the advance, we 

 can only say that specially favourable physiological conditions 

 prevailed in their case, such, in fact, as we have seen to result 

 from progressive Symbiosis. We may say apparently in 

 accordance with Prof. Wood Jones's own intuitions that 

 " right " function produced the good result. It seems a pity that 

 " partnership " as a means of progressive change has not yet 

 apparently found a place in Prof. Wood Jones's scheme. In 

 Symbiogenesis I have referred to Darwin's statement that 

 " the brain must be bathed by warm blood in order to be highly 

 active, and this implies aerial respiration," and I have there 

 endeavoured to show that an important connection exists 

 between respiration and food. The better the food bio-econom- 

 ically considered the better the respiration. It has been 



