EVIDENCE FROM BLOOD TESTS 127 
6. A close relationship is shown to exist between all marsupials, 
with the exception of the Thylacine, or so-called Tasmanian Wolf. 
7. Strong anti-turtle serum gives maximum reactions only with 
the bloods of turtles and crocodiles; with those of lizards and snakes 
the results are almost negative. With the egg-albumins of reptiles 
and birds a moderate reaction is given. ° 
8. Anti-lizard serum produces maximum results with the bloods 
of lizards and reacts well with those of snakes. 
g. These experiments indicate that there is a close relationship 
between lizards and snakes, on the one hand, turtles and crocodiles 
on the other. They further indicate that birds are more nearly allied 
with the turtle-crocodile series than with the lizard-snake series, 
results for which palaeontological studies had already prepared us. 
to. “Tests were made by means of anti-sera for the fowl] and 
ostrich upon 792 and 649 bloods respectively. They demonstrate a 
similarity in blood constitution of all birds, which was in sharp con- 
trast to what had been observed with mammalian bloods, when acted 
upon by anti-mammalian sera. Differences in the degree of reaction 
were observed, but did not permit of drawing any conclusions.” 
11. I have already called attention to the fact that the prob- 
lematical Horseshoe-crab is indicated by its embryology to be related 
to the air-breathing spiders and scorpions rather than to the marine 
Crustacea. It is of exceptional interest to learn that embryology is 
supported by the results of the blood tests. 
It must not be supposed that there is any exact mathematical 
ratio between the degrees of relationship indicated by the blood tests 
and those which are shown by anatomical and palaeontological 
evidence. Any supposition of the kind would be immediately nega- 
tived by the contrast between the blood of mammals and that of birds. 
It could hardly be maintained that an ostrich and a parrot are 
more nearly allied than a wolf anda hyena and yet that would be 
the inference from the blood tests. Like all other anatomical and 
physiological characters, the chemical composition of the blood is 
subject to change in the course of evolution and these developmental 
changes do not keep equal pace in all parts of the organism. It is the 
rule rather than the exception to find that one part of the structure 
advances much more rapidly than other parts, such as the teeth, the 
skull, or the feet. The human body is, fortunately for us, of rather 
a primitive kind, while the development of the brain is far superior 
to that of any other, mammal and this great brain development has 
