496 THE ORIGIN OF VERTEBRATES 
the vertebrate organs is absolutely hypothetical, no clue is given in 
Balanoglossus, not even to the segmented nature of the vertebrate. 
The same holds good with the evidence from Embryology and from 
Paleontology. I have pointed out how strongly the evidence in both 
cases confirms that of Comparative Anatomy. In neither case is the 
strength of the evidence for Balanoglossus in the slightest degree 
comparable. In Embryology an attempt has been made to compare 
the origin of the ccelom in Amphioxus and in Balanoglossus. In 
Paleontology there is nothing, only an assumption that in the 
Cambrian and Lower Silurian times a whole series of animals were 
evolved between Balanoglossus and the earliest armoured fishes, which 
have left no trace, although they were able to hold their own against 
the dominant Paleostracan race. The strangeness of this conception 
is that, when they do appear, they are fully armoured, as in Pteraspis 
and Cephalaspis, and it is extremely hard luck for the believers in 
the Balanoglossus theory that no intermediate less armoured forms 
have been found, especially in consideration of the fact that the 
theory of the origin from the Paleostracan does not require such 
intermediate forms, but finds that those already discovered exactly 
fulfil its requirements. 
One difficulty in the way of accepting the theory which -I have 
advocated is perhaps the existence of the Tunicata. I cannot see 
that they show any affinities to the Arthropoda, and yet they are 
looked upon as allied to the Vertebrata. I can only conclude that 
both they and Amphioxus arose late, after the vertebrate stock had 
become well established, so that in their degenerated condition they 
give indications of their vertebrate ancestry and not of their more 
remote arthropod ancestry. 
In conclusion, the way in which vertebrates arose on the earth as 
suggested in this book carries with it many important far-reaching 
conclusions with respect to the whole problem of Evolution. 
When the study of Embryology began, great hopes were entertained 
that by its means it would be possible to discover the pedigree of 
every group of animals, and for this end all the stages of development 
in all groups of animals were sought for and, as far as possible, 
studied. It was soon found, however, that the interpretation of 
what was seen was so difficult, as to give rise to all manner of views, 
depending upon the idiosyncracy of the observer. At his will he 
decided whether any appearance was ccenogenetic or palingenetic, 
Ee as 34 
