214 SYMBIOSIS 



making the attempt to leave the water at all ? What biological 

 factors proved helpful, and what kind of physiological ground- 

 work was it on the whole that, even apart from all volition, 

 prepared the way to the emergence of progressive terrestrial 

 adaptation ? 



Of the Amphibians, which play so great a part in Prof. Wood 

 Jones's study, we know that the tadpoles are mostly cross-feeders 

 (feeding largely on algae). The Batrachians, moreover, excel by 

 a comparatively high degree of parental sacrifice ; all of which 

 is of the highest physiological importance. Many Amphibians 

 have remained strict cross-feeders to this day. We may 

 conclude that in the case of aquatic cross-feeders, a successful 

 evolution of the limbs was powerfully supported by an auspicious 

 f/w ratio, entailing balance and orientation generally. To obtain 

 the fullest biological support, whilst yet remaining moderate 

 and balanced, this we have found to be the great pre-requisite 

 of progressive evolution, and there is nothing in Anatomy to 

 invalidate our conclusion. Such desiderata we have found to 

 be in the path of Symbiosis and of Symbiosis alone. 



In the absence of a Qualitative Biology to enlighten us with 

 regard to what constitutes ' ' normal specialise tion , ' ' or even normal 

 physiological or biological development, the author quite naturally 

 is confined to the records of Palaeontology as, to him, the only 

 likely sources of information with regard to origins. Above all 

 he points to the curious group of animals known as the Therapsida, 

 which, " presenting a blend of primitive reptilian and primitive 

 mammalian characters, flourished in the Triassic period." 



And he says further : "It was, according to Broom, among 

 the South African members of the Therapsida especially that the 

 limbs became supporting organs, and he has said very definitely 

 that " when the Therapsidian took to walking with its feet under- 

 neath and its body off the ground it first became possible for it 

 to become a warm-blooded animal." The change that we have 

 been picturing was, therefore, one which took place very far back 

 in the geological past ; and, according to Broom, the supporting 

 limb and the mammalian possibilities made their appearance 

 together, the one being dependent upon the other. The characters 

 of the supporting limb as opposed to the purely propelling, but 

 not supporting, limb, are so definite that there should be but 

 little hesitation on the part of an anatomist in assigning the proper 

 functions to the limbs of anv extinct form." 



