F. B. Cowper Reed — Blind Trilohites. 555 



detection of enemies, or the capture of prey, and were correlated 

 with a lack of agility ; at any rate the evidence is antagonistic 

 to supposing that they signify deep-water conditions. It should 

 be observed also that the character of the fauna associated with 

 these large-eyed genera varies much, as we may at once see 

 in examining the lists of organisms from the beds in which they 

 occur. 



It is a remarkable fact that in the case of such deep-sea deposits 

 as the Culm beds which are associated with the Radiolarian cherts 

 of Devonshire,' none of the trilobites show degeneration or abnormal 

 development of their eyes. 



The highly - developed trilobites sueh as Encrinurus, Cyhele, 

 Acidaspis, many species of Phacops, etc., which possess eyes smaller 

 than the average, are not found in deposits or with associated faunas 

 suggestive of deep-sea conditions. We have also no reason to 

 suppose that those species of Phacops and Proetus with unusually 

 large eyes lived in the abysses of the ocean, for the lithological 

 character of the deposits and the features of their contemporaneous 

 faunas point usually to the existence of shallow water. 



Conditions of Life of Blind Trilohites and Comparison loitli Modern 

 Blind Crustacea. 



The most popular and widely accepted view of the conditions under 

 which the blind forms lived is that put forward prominently by Suess, 

 Neumayr, and others. They suppose that these forms existed under 

 deep-sea conditions, and that the partial or complete absence of 

 light in the abysses of the ocean led either to the reduction or loss 

 of the visual organs or to their enlargement to an extraordinary 

 degree. In the first place, before we test this theory and see how 

 far it satisfies the facts of the case, we must remember that it is 

 a theory of adaptation and therefore cannot be applied to those 

 genera which, as we have seen, could never have possessed compound 

 eyes because of their low phylogenetic rank. Accordingly we have 

 to exclude all the genera of our Group 1, for we have shown that we 

 cannot even consider the post-Cambrian primitive blind forms as 

 surviving on account of a maintenance or repetition of an identical 

 biological or physical environment, but rather because they occupied 

 a place in the economy of nature which higher forms could not 

 fill. The survival of all primitive and lowly forms of life at the 

 present day appears to be due to this cause.^ 



We must therefore consider that all theories of adaptation are only 

 applicable to our Group 2, which consists of what we have called, 

 a priori, the adaptive blind forms, because their blindness is an 



1 G. J. Hinde : Q.J.G.S., vol. li (1895), p. 609; Trans Dev. Assoc, vol. xxvi'" 

 (1896), p. 747 ; ibid., vol. xxis (1897), p. 518. 



2 Suess (" Antlitz der Erde," vol. ii, p. 274), however, regards the oldest kii''' •■ 

 fauna of the Bohemian Silurian beds (i.e. E'tage C) to be an ' adapted' fauna'^^ 

 therefore the successor of a still older and unknown fauna. But he seems to^hales 

 at this opinion by neglecting the testimony of phylogeny and ontogeny, . ■ , 

 regarding the absence of eyes in every case necessarily as an adaptive feature^T^ n o' 



