6 
ORGANIC DEPENDENCE AND DISEASE 
the existence and earliest appearances among these ele- 
mentary expressions of life, of conditions which show an 
actual mutual dependence of creatures one upon another; 
that is to say, of the conditions commonly known variously 
as symbiosis, mutualism and parasitism. Such evidences 
are not easy to acquire among primitive forms of life as 
preserved in the rocks of the earth’s historic record, but 
persistent and long-continued search with the aid of a va- 
riety of special procedures adapted to the extraction of the 
peculiar character of the material employed, enlarged by 
the inspection of many great museum collections and joined 
with the help of generous colleagues and the special sup- 
port of the National Academy of Sciences, has resulted in 
even so much light on these significant paleopathologic 
problems as is here set forth. 
The writer desires to present his facts without embar- 
rassing detail and his conclusions without bias. In his own 
justification for both he may urge a long acquaintance with 
nature’s modes in the preservation of such materials in the 
fossil state and reasonable familiarity, based upon com- 
parative morphology, with the forms of life that go to make 
up the earlier faunas and floras of the earth. 
It will be observed, and special emphasis is put on this, 
that these chapters deal with the lower forms of life, the 
invertebrates among animals and cryptogams among the 
plants. The actual outstanding evidences of pathological 
and traumatic lesions among extinct animals of the verte- 
brate type are not comprehended within this discussion as 
such phenomena are registered only among faunas of the 
earth too late and too specialized for our consideration. 
Such lesions have been noted by several students of verte- 
brate paleontology and most interestingly brought together 
by Dr. Roy L. Moodie, whose investigations into the history 
of such registered conditions and of the possible effect of 
disease in the extermination of races of the higher animals 
through the later ages of the earth are very suggestive to 
