274 H. BALDWIN WARD 



This observation attracted the attention of Leuckart, who in liis 

 monograph gives due crédit to Leidy, and suggested tliat tricliinosis 

 in Man might iDe due to the eating of raw Porlv containing the 

 parasite. One of the most important of his early helniinthological 

 contributions (1) contains ideas which retlect clearly those advan- 

 ced by Darwin in the Origin of Species five years later. Leidy says ; 

 « The study of the earth's crust teaches us that very many species 

 of plants and animais became extinct at successive periods, while 

 other races appeared to occupy their places. This was probably the 

 resuit in many cases of a change in exterior conditions incompa- 

 tible with the life of certain species and favorable to the primitive 



production of others Living beings did not exist upon the 



earth prior to their indispensable conditions of action, but where- 

 ver thèse hâve been brought into opération concomitantly the 

 former originated. . . . Of the life présent everywhere with its 

 indispensable conditions and coeval in its origin with them, what 

 Avas the immédiate cause ? It could not hâve existed upon the 

 earth prior to its essential condition and it is therefore the resuit of 

 thèse. There appear to be but trifling steps from the oscillating 

 particle of organic matter to a Bacterium, from this to a Vibrio, 

 thence to a Monas, and so gradually up to the highest of life ! The 

 most ancient rocks containing the remains of living beings, indi- 

 cate the contemporaneous existence of the more complex as well 

 as the simplest of organic forms ; but, nevertheless, life may hâve 

 been ushered on the earth through océans of the lowest type, long 

 previously to the deposit of the oldest paleozoic rock as known 

 to us ! ! )) 



A séries of helminthological contributions ran from 1830 to 1856 

 culminating in his Synopsis (2), which is the only paper of its kind 

 that has yet appeared in this country. Then the pressure of paleon- 

 tological work seems to hâve put ofï his studies on parasites, for 

 with the exception of occasional notes, nothing was published 

 until 1875. Among thèse fragments, however, may be noted one 

 of the earliest comments on the agency of Flies in communicating 



(1) A Fauna and Flora within living animais. Swithsonian Contributions to 

 knowledge, V, 1853. 



(2) A Synopsis of Entozoa and Some of the Ectocongeners. Proceedings of t/ie 

 Academy of nat. se. Philadelphia, VIII, p. 42-50, 1856. 



