240 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



ologists have hitherto been following a Will-o'-the Wisp, 

 and that the sense organs they have been tracing do not 

 become the lateral sense organs of the adult. This, as 

 an error of interpretation, would certainly be welcome 

 news if true, since it is difficult to conceive that so many 

 eminent morphologists should have been mistaken in their 

 facts, and it would, of course, at once explain why the 

 anatomical and embryological views should have been 

 so widely different. It is stated that the sense organs 

 described by embryologists belong to an altogether different 

 system, which is perhaps metameric, which possibly 

 corresponds to the segmental sense organs of invertebrates, 

 and which degenerates in the adult. It is, therefore, very 

 probable that the development of the lateral organs, when 

 described, will be found to exactly tally with their adult 

 relations, and to conform with the views previously 

 stated. 



In the branchial nerves it is obvious that we have more 

 primitive structures -than is the case with the lateral 

 nerves, since they represent the modified nerves of the 

 anterior extremity of the ancestral form, and have under- 

 gone far less differentiation both as regards bulk and 

 nature. The lateral nerves cannot have been represented 

 in the archaic vertebrate by more than a few bundles of 

 somatic sensory fibres, for the majority of the fibres of 

 the anterior nerves went to form what we now know as 

 the branchial nerves. That the branchial nerves represent 

 modifications of the primitive type follows as a logical 

 necessity, but the modification was perhaps more physio- 

 ogical than anatomical, and consisted rather in the 

 differentiation of fibres than in the formation and arrange- 

 ment of nerve trunks. 



A visceral arch of a fish is supplied by one afferent 

 vessel, drained by two efferents, and innervated by two 



