4i2 COMPARATIVE ZOOLOGY OF CHORDATES 



Some of the most interesting results are those which refer 

 to the relative affinities between the various groups of reptiles, 

 and between them and the birds. 



Anti-fowl egg serum mixed with blood of : — 



Crocodile, gave a positive result (precipitation) in 50 per cent, of cases. 

 Chelonian ,, ,, ,, ,, 40 ,, ,, 



Lacertilian ., ,, ,, ,, 7 ,, ,, 



Ophidian ,, „ ,, ,, 6 ,, ,, 



These results show that the reptiles (alive now) nearest akin 

 to the birds are the crocodiles, which again corroborates all 

 the evidence from other sources. It further indicates that the 

 crocodiles and turtles are more closely akin to one another 

 than they are to the lizards and snakes, which, again, are fairly 

 closely allied to one another. This is further shown by the 

 following : — 



Anti-chelonian serum mixed with blood of : — 



Chelonian gave a positive result in 87 per cent, of cases. 

 Crocodile „ „ „ 25 



Lacertilian ,, ,, ,, o „ ,, 



Ophidian „ ,, ,, 6 „ ,, 



Besides the precipitin tests, there are other methods of 

 estimating the blood-relationships of vertebrates. For one 

 thing, it is found that blood of any particular species has the 

 power of destroying the blood-corpuscles of other species, 

 to an extent varying with the remoteness of the relationship 

 between them. Again, it is found that the degree of virulence 

 with which an animal will suffer from a human disease varies 

 with its degree of kinship to man. So syphilis attacks the 

 chimpanzee more seriously than the orang, and the latter more 

 than the baboon. Lastly, attention may be called to the 

 so-called blood-groups, into which the human race is divided. 

 There are four of these blood-groups, and they are due to two 

 agglutinating substances, which may be absent, or one, or the 

 other, or both may be present, in the blood of a man, and 

 cause clotting when the blood is mixed with that of another 

 incompatible group. Incidentally these groups are further 

 interesting in that there is reason to believe that they are 

 inherited by means of Mendelian factors, but their main 



