TOO AN INTRODUCTION TO SCIENCE 



are similar to those of the median eyes of invertebrate ani- 

 mals. Lastly, to touch upon the question of the new mouth 

 of vertebrates : the anterior part of the new gut was originally 

 a respiratory chamber, which afterwards served as an ali- 

 mentary canal. This respiratory chamber was formed, as 

 it is now formed in the scorpion group, by the insinking of 

 respiratory apparatus, which in other arthropods, such as lob- 

 sters, stand out on the under side of the head. Indeed the 

 nearest approach which we can make to picturing our ances- 

 tor in the direct line at the point at which the vertebrate and 

 the invertebrate sub-kingdoms branched off, is to represent 

 him as resembling one of the old extinct sea-scorpions ; and 

 the earliest animal for which we can find a place in our 

 pedigree after the separation took place is the earliest known 

 fish thycotis, which is found in Upper Silurian strata. This 

 fish belongs to a long extinct group, the cephalaspids, which 

 present many points of resemblance with the lowest of exist- 

 ing fishes, the lamprey in its larval stage ; while, on the 

 other hand, they show many indications of kinship with the 

 trilobites and old sea-scorpions. 



Dr. Gaskell's views, which he has advocated with great 

 persistency and ingenuity, have been much discussed at 

 recent meetings of the British Association and other scien- 

 tific societies. The majority of zoologists are opposed to 

 them, but, even if it were otherwise, it would be going be- 

 yond our province to express an opinion upon any hypothesis 

 which is still under discussion. We wish to introduce the 

 reader to the problems which are occupying the attention of 

 scientific men without prejudicing his judgement ; and 

 certainly no more striking illustration of the profound change 

 which Darwin's doctrine has effected in biological thought 

 could be cited. This missing chapter in the history of the 

 animal kingdom has to be written, but no one thirty years 

 ago would have ventured on so bold a rendering. 



The biologist first observes and collects. He then 

 classifies, empirically to begin with, but according to prin- 



