464 
president’s address. 
Bunge and Quinton, has come to the conclusion that “the 
blood plasma of vertebrates and invertebrates is, in its inorganic 
salts, but a reproduction of the sea water of the remote 
geologic period in which the prototypic representative of such 
animal forms first made their appearance.” 1 In the verte- 
brates, whether aquatic or terrestrial, the blood has an almost 
constant osmotic pressure and salinity, and Macallum assumes 
that this salinity reveals to us the composition of the sea water 
at the period of their origin. Though, for various reasons, 
such conclusions cannot be accepted, it does seem extremely 
probable that the relatively high salinity of the internal fluids 
of fresh water invertebrates is the indelible imprint of the 
original marine environment. 
The most satisfactory hypothesis of the origin of life in the 
sea is that of Brooks, J according to which all life was confined 
at the outset to the pelagic regions of the deep sea, where 
uniform conditions prevailed and the struggle for existence was 
relatively slight. Here gradually the main lines of animal 
form were laid down. Later the littoral regions were colonised, 
and here the varied surroundings and strenuous conditions of 
life were potent stimuli to rapid evolution. 
An effective colonisation of the littoral region is naturally 
precedent to a migration into fresh water, and it is therefore 
only to be expected that all the main types of structure had 
been evolved before this immigration took place. Consequently 
we should not expect, and do not find, that fresh water contains 
any group of organisms markedly distinct from their nearest 
relatives in the sea. The fresh water fauna is, in fact, a 
selection from that of the sea, and not one that has evolved in 
fresh water on distinct lines. 
The wide distribution of fresh water animals of certain 
classes indicates a very ancient establishment, and there are 
preserved to us in fresh water some forms of very archaic 
nature. The Phyllopod Crustacea, for example, are spread 
over the whole globe, and represent the most primitive type of 
1. Macallum. Trans-Canadian Institute. VII., 1901. 
2. Brooks. Foundations of Zoology, 1899, p. 215. 
