196 Kepoet of the State Geologist. 



not e^ist complete obscurity, since many animals are phos- 

 phorescent; some, like the Fishes, have even special luminous 

 organs which enable them to illuminate themselves. But the 

 light in certain regions is often very feeble. In these conditions 

 a double adaptation may intervene; sometimes the organs of 

 sight assume a considerable size, as is the case for the Fishes of 

 the genus Ipnops, and among the Crustaceans of the genus Cysto- 

 ^oma where the eyes cover the entire upper surface of the head ; 

 sometimes, on the contrary, the eyes are rudimentary, or even in 

 some cases disappear altogether after having been represented 

 in embryonic life ; this occurs with Fecten^ various Gasteropods, 

 and a great number of decapod Crustaceans. These last-named 

 animals supply the absence of the visual organs by an extreme 

 development of the appendages which transform themselves into 

 organs of touch. 



But these interesting facts are not without analogies in the 

 -ancient epochs. The Trilobites of the Cambrian period show 

 this same mixture of almost or quite blind forms {Agnostus, 

 Trinucleus\ and of forms provided with unusually large organs 

 of sight {JEglina). 



Barrande has even shown that a species blind in the adult state 

 {Trinucleus BucMandi) possessed normal eyes in its early age ; 

 sometimes even (various 'forms of Paradoxides) .the ocular 

 peduncle remains while the sensorial part is wanting, which actu- 

 ally occurs in the deep water Cymonomus. This proves at 

 least that the forms in question existed in conditi> -ns where the 

 light was distributed in the same way as it is at present in the 

 profound depths Still other particularides, as the absence of 

 strictly littoral forms and also the absence of the primordial 

 forms of the diverse groups which appeared later Suddenly and 

 in an advanced condition of differentiation, lead us to think that 

 the marine forms of moderate depths were very clearly defined, 

 and that we do not as yet know what was the the littoral facies 

 of the Cambrian, or at least the fauna which characterized it. 

 {Suess, ISTeumayr.) This opinion, it must be stated, is not 

 accepted by the majority of French palaeontologists. 



It has been supposed that in the chalk deposits the formations 

 of the deep sea would be found ; but we have seen that the anal- 

 ogy of certain fossils of that age with the fauna of the present 

 Verticordia-zonQ proves nothing; the organisms of that epoch 



