BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. 95 
The System of Branchial Sense Organs and their 
Associated Ganglia in Ichthyopsida. A Con- 
tribution to the Ancestral History of Ver- 
tebrates. 
By 
John Beard, Ph. D., B.Sc., 
Berkeley Fellow of Owens College, Victoria University, Manchester. 
With Plates VIII, IX, and X. 
INTRODUCTION. 
Amone the many weighty questions which have arisen with 
the rise and progress of comparative embryology, that of the 
origin and ancestral history of Vertebrates has occupied, and 
still occupies, an important place. 
That the question, if capable of solution at all, would be 
solved by the discoveries of embryology is now, and has been 
for the last ten years, a general opinion among zoologists, 
So much for a general agreement. But as to the particular 
line of descent one might recall half a dozen different theories 
supported by different schools of workers. 
The impulse to these speculations was first given by the 
discovery of the tadpole-like larva of Ascidians, and the opinion 
that Vertebrates were derived from Ascidians we owe to 
Kowalevski and Kupffer. This view has had its day, and is 
now only a reminiscence. 
Another important theory, important because clothed with 
the authority attached to the name of Balfour, is the theory 
that Vertebrates arose from unsegmented worms, in which two 
