XXX Journal of Comparative Neurology. 



which they supply ; yet it will not do at present to affirm that a nerve 

 can never supply an organ which has originated out of its own meta- 

 mere. In other words, the innervation of an organ cannot in the 

 present state of our knowlege be taken as an infallible guide to its 

 metamerism. It is, of course, possible that subsequent research may 

 remove the apparent exceptions. Fiirbringer's attitude on the ques- 

 tion is explained by his unswerving devotion to the neuromuscular 

 theory, to which he devotes a section in the appendix. 



At the conclusion of the summary of the first and second sec- 

 tions, which deal with the Seiachii and the higher vertebrates respec- 

 tively, a few genealogical considerations are adduced. The arrange- 

 ments of these organs in the vertebrates support in general the ac- 

 cepted taxonomy. Among the Seiachii the Notidanidse are the most 

 primitive, the bony fishes connect with the ganoids through amioid 

 forms, the Dipnoi occupy a quite isolated position, the Amphibia con- 

 nect with the Crossopterygia, and the Urodela and Gymnophiona are 

 more primitive than the Anura. The Myxinoidae are far separated 

 from the Petromyzontidse are given a class by themselves. 



The third section contains an exhaustive study of the first spinal 

 nerves of the cyclostomes and Amphioxus, which leads to the con- 

 clusion that the third or fourth spinal nerve of Petromyzon is homo- 

 logous with the first of the Notidanidae, while the myxinoids possess 

 three spinal nerves which lie cephalad of the first of Petromyzon. This 

 latter condition is regarded as a primitive one, and it follows that the 

 lowest selachians have already lost five or six of their spinal nerves. 



The leading motives of this third section are suggested by two 

 questions of fundamental importance : 



(i) The general homology of cranial and spinal nerves and in 

 particular. What is the relation between the viscero-motor nerves of 

 the head (V, VII, IX and X + XI) and the somatic motor nerves of 

 the head (III, IV and VI) and between these nerves and the motor 

 nerves of the trunk ? 



(2) Are the most cephalic spinal nerves of cyclostomes, which 

 appear to have been losi in all higher forms, perhaps represented in 

 the III, IV(?) and VI nerves; and, if so, were these nerves origin- 

 ally spinal nerves which have secondarily migrated into the head, or 

 were they from the first pre-vagal (paleocranial) nerves ? 



Under the first head, the author's attempt to dismiss the sensory 

 nerves with the off-hand remark that the general homology of cranial 

 and spinal sensory nerves is scarcely controverted, we have already 



