xvi Journal of Comparative Neurology. 



by dichotomous division between the epithelial cells. The nerve fib- 

 ers do not reach more than two thirds of the way through the thick- 

 ness of the epithelium. These branched termini now become more 

 bushy and finally grow up and enclose the bases of the specific audi- 

 tory cells. In older embryos (24-30 mm.) the terminal apparatus is 

 more highly developed and is closely applied to the auditory cells, 

 though there is not protoplasmic continuity. This stage too shows a 

 difference between the termini of the maculae and the cristae acusti- 

 cae, the former consisting of very numerous delicately branched fib- 

 rils, the latter of few, thick, short branches. The same method ap- 

 plied to the mammals gave essentially similar preparations. 



These results with the methylene blue obviously harmonize very 

 closely with those of Retzius, von Lenhossek and others with the 

 chrome-silver method. c. j. h. 



The Homologies of the Hypoglossus Nerve in Lower Vertebrates. 



This old problem about which so much has been written and so 

 little known in the past is clearly reaching the point where speculation 

 ceases and legitimate generalization begms. Kupffer's recent extend- 

 ed review ' has done much to clarify the matter and to indicate the 

 gaps m our knowledge which require further investigation. The two 

 groups most in need of further study seem to be the cyclostomes and 

 the bony fishes. In the case of Petromyzon, it will be remembered 

 that the ventral musculature of the head is innervated from the vagus, 

 not from the first spinals, or " hypoglossus," as in most of the other 

 lower vertebrates. Kupffer was of the opinion that this ventral mus- 

 culature is not derived from the lateral musculature, as is the case 

 with the " hypoglossus musculature" of other vertebrates; but that it 

 is of dermal origin. Hence the difference in its mode of innervation. 



The matter has been re-studied under Kupffer's direction by Dr. 

 H. V. Neap with quite a different result. Dr. Neal finds that this 

 ventral musculature is developed in Petromyxon in exactly the same 

 way as in the gnathostomes and is homologous throughout the verte- 

 brate series. The ramus recurrens vagi of Petromyzon is therefore 

 homologous with the hypolossus of higher vertebrates, while the so- 

 called hypoglossus of the older writers on Petromyzon is composed of 

 true spinal nerves. 



1 In Merkel und Bonnet's Ergebnisse for 1895, pp. 607-618. 



'The Development of the Hypoglossus Musculature in Petromyzon and 

 Squalus. Anat. Anz., XIII, 17, 1897, pp. 44I-463. 



