ORIGIN AND EVOIATION OF LIFE 609
just above the freezing point, and to total absence of light which is compensated for by the evolutioo of a great variety of phosphorescent light prodacing organ?.' Another extreme of chemical evolution among
���the fishes is the production of electricity as a protective function, which is even more effective than hony armature i)ecause not interfering with lapid motion. In only a few of the fishes is electricity generated in sufficient amounts to thoroughly protect the organism. It develops through modified body tissues in the form of suj>erimposed plates
��REVEnSED EVOLUTION O
���Fia. 18. <Left.) Direct Ohiginai. Evolution of the Bone
�R OP THE LOBB-
�FIN or A F18II (A, B) (RMpldittIa type of Cop*) Into the bonj. On
�■-ruyed Umb <C)
�ot the Ampblblnn of the Carbonlferoua age.
� �(RiQHT.) SECOSDiRi Revebsed Bvolutioij OF THE Fmt-niveD
� �Reptile (A) Into the On, oc paddle {B, C) ot an Uhlhyo«aur.
� ��(electroplates) separated equally from one another by layers of a peculiar jelly-like connective tissue, all lying parallel to each other and at right angles to the direction of discharge. The electric organ is formed from modified muscle and connective tissue and is innervated by motor nerves. The physical principle involved is that of the con- centration cell, and the electrolyte used in the process is prol)ably so- dium chloride. The theory is that at the moment of discharge a mem- brane is formed on one surface of the electroplax which prevents the negative ions from passing through while the positive ions do pass ' The author is especiall}' mdebt«d to Professor Ulric Dalilgren, of Princetoa TTniverBity, for notes upon phosphorescent and electric organs.
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