554 F. R. Cowjier Reed — Blind Trilobites. 



brachiopods with only rare representatives of other groups. In so 

 far as this argument affects our subject of consideration we may 

 remark that (a) a variety of types is not necessarily demanded in 

 such an early geological period ; (6) an impoverished fauna is 

 capable of several other explanations than deep-sea conditions, as 

 for instance the Permian. The superabundance of two such groups 

 of organisms as trilobites and brachiopods is not of much value as 

 evidence, since one group is extinct and the other is by no means 

 characteristic of the deep sea {Lingula, the oldest surviving type, 

 being in fact an inhabitant of shallow water). 



(3) The almost complete want of organisms with skeletons of 

 carbonate of lime. To this the reply may be made that modern 

 deep-sea deposits consist largely of carbonate of lime, and are 

 mostly composed of the remains of animals that secreted carbonate 

 of lime, with the exception of the Eadiolarian Ooze and Eed Clay, 

 to which few, if any, Cambrian trilobite-bearing deposits can be 

 compared except by neglecting many chai'acteristic features or 

 making unwarrantable assumptions. 



(4) The occurrence of blind and large-eyed animals. If we 

 leave out of the question the disputed Paradoxides and allies, all 

 the blind genera which Neumayr here refers to are devoid of eyes 

 because of their phylogenetic position, as we have shown. Neumayr 

 regards all these forms as having lost their eyes by a secondary 

 modification, and quotes Trinuchus Bucklandi, which as we have 

 remarked possesses visual organs when in a larval stage, but loses 

 them at maturity. But these are eye-spots and not compound eyes, 

 and are not characteristic of any phylogenetic stage. Their significance 

 has been discussed above. An example which has been supposed^ 

 to be similar (but is probably not so, as the eyes are of the normal 

 crustacean type) is that of the deep-sea decapod Willemcesia, the 

 embryo of which is said to possess well-developed eyes. The 

 eyes of the larval Trinuchus, on the other hand, are not normal 

 trilobite eyes. Neumayr also lays stress on the association of blind 

 and large-eyed forms. But we have just dismissed the majority of 

 blind ones from the question, and have seen that they are to be 

 explained in a totally different manner, resting on the ascertained 

 facts of phylogeny and ontogeny, and not on theoretical con- 

 siderations. So the occurrence of the large-eyed forms such as 

 jEgJina and Bemopleiirides must be dealt with alone. The great 

 development of visual organs, though a striking character in many 

 deep-sea Crustacea (e.g. Ci/stisoma neptunus) and other deep-sea 

 organisms, is not confined to them ; nocturnal and cave-frequenting 

 animals have extraordinarily developed powers of sight, and, as we 

 have mentioned, Barrande indeed suggested the muddiness and 



\therefore comparative shallowness of the water in which these 

 t^rilobites lived as a sufficient cause. But the large-eyed Beino- 

 ^i^urides frequently occur in limestones which accumulated in clear 

 oorr«r. Perhaps the large eyes served simply for the better 

 blind 

 ar- ■" 1 W. Marshall, " Die Tiefsee imd ihr Tierleben" (Leipzig, 1888), p. 265. 



