244 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



ment, is admirably shown by an examination of the 

 lateral line nerves of fishes. In the Holocephali, which we 

 know palaeontologically to represent archaic forms, and 

 therefore, perhaps, show us the nerves in a fairly primitive 

 condition,* the lateral line nerves arise from a series of 

 independent roots, which, in only one case, are confused 

 with the roots of any of the other nerves. The facts, 

 therefore, here go to show that the lateral sense organs 

 are supplied by a number of nerves, which, being entirely 

 confined to this purpose and almost entirely distinct from 

 the remaining cranial nerves, we cannot conceive as 

 existing apart from the sense organs themselves, and, 

 indeed, only as a few somatic sensory fibres confined to 

 the region from which the lateral sense organs were primi- 

 tively differentiated. An examination of other forms shows 

 that the condition in the Holocephali represents only the 

 first chapter of the tale, the last being, as illustrated by 

 the specialised Teleosts, the condition in which the lateral 

 line nerves have become completely incorporated with one 

 of the remaining cranial nerves, notably the facial. We 

 may infer that the Holocephalous type is the more primi- 

 tive one, because Palaeontology teaches us that as regards 

 their skeletal structure they have departed less from their 

 Palaeozoic ancestors than the specialised Teleosts. Hence 

 we have two extremes — a primitive extreme, in which the 

 lateral line nerves arose separately from the brain and 

 formed four independent nerves; and a specialised extreme, 

 in which these four nerves have finally become more or 

 less fused with the seventh or facial nerve. If we 



* But liow far is it permissible to take a series of recent forms, arrange them 

 in a certain order, and then claim that they represent stages between one 

 type and another? All recent forms are ultimate products and. not stages, 

 and how are we to know that certain of them are slightly more primitive 

 than others ? The only direct evidence is based on the preservation of hard 

 parts. 



