134 AYERS. [Vol. VI. 



The rami maculi and sacculi are further divided peripherally 

 into numerous small branches, arranged in comate or pectinate 

 order as the case may be. 



This breaking up of these important nerve branches is in 

 harmony with the growth of the sense organs to which they 

 run. As Retzius has shown, the nerve branches to the maculae 

 acusticae utriculi and sacculi are broken up into several or many 

 branchlets almost as soon as they become distinct from the 

 main trunk ; nevertheless, they are to be considered together as 

 forming a single branch. Retzius has not mentioned, however, 

 that in some of the lower forms (Elasmobranchs) the nerve con- 

 tinues its trunk out to the distal portion of the sense organ it 

 supplies, and gives off a series of branchlets all the way along. 

 This mode of branching is to be considered the primitive one, 

 since it agrees with the method followed by the nerves supply- 

 ing long canals on the surface of the body, and the form de- 

 scribed by Retzius is doubtless a secondary modification of it. 



The form I have just described is produced in ontogeny by 

 the rapid division of the sense organ in a linear direction 

 and the breaking up of the nerve to supply the individual sense 

 organs, which have thus become separated by short intervals 

 from each other. This method of nerve branching is, so far as 

 essentials are concerned, found in both the large, compound 

 sense organs of the ear, viz. the macula utriculi and the cochlear 

 organ. 



Taking the groups serially, we find many interesting varia- 

 tions, which are, however, relatively unimportant from the mor- 

 phological standpoint. 



The auditory nerve in this group of fishes has the usual two 

 branches which pass to the canal complexus at its inner anterior 

 and inner posterior ends. The first-named branch is the ramus 

 utricularis, and supplies the anterior division of canal organs. 

 It divides into two main branches, the anterior ampullar and 

 the utricular nerves. The former divides into two portions, 

 one of which supplies the anterior canal sense organ, while the 

 other passes on to that of the external canal. The second- 

 named branch passes to the utricular sense organ and divides 

 into as many discrete branchlets as there are sense organs in 

 the group. The posterior branch is the ramus saccularis, and 

 supplies the macula acustica sacculi and gives off a branch to 



