ILect. IV. SPECIALISATION OP LOW TYPES. 91 



In the latest paper on the Vertebrata for which I am 

 responsible, namely, that on Marsipobranch Fishes 

 {Lamprey and Hag), just published in the Philosophical 

 Transactions, I have ventured to state that the lowest 

 known fish — the Hag — is as much specialised for its 

 own kind of life, as man himself is, for his. In some of 

 my former Lectures I showed in detaU the extreme 

 modification, for special purposes, seen in the structure 

 of Serpents. 



Now Serpents are always reckoned to be the lowest 

 of the Eeptilian class ; they are indeed degraded forms, 

 going on their belly, because they have lost their legs, 

 and eating dust with their meat because of their help- 

 lessness. But if nature has taken from them with one 

 hand, she has freely imparted her gifts to them with 

 the other, and their spine and skull beggar all other 

 forms of animal mechanism. 



There has been plenty of time for both loss and gain 

 in the ascent of the various existing forms from their 

 simple, metamorphosing, hypothetical ancestors ; and in 

 the countless ages during which this agonistical wrest- 

 ling for life has gone on, changes have taken place that 

 we are only slowly beginning to conceive of. Tens of 

 thousands of types have fainted and failed, and have 

 <lropped out of the race and out of the conflict ; of these, 

 here and there, a word may be read in the leaves of 

 the old stony book. Others, however, wrestled until 

 they were almost exhausted ; nevertheless, they held 



