1 86 AYERS AND JACKSON. [Vol. XVII. 



vertebrates. Not a few papers have dealt with the comparative 

 anatomy of the myxinoid fishes ; but the authors of these papers, 

 almost without exception, have drawn their anatomical knowl- 

 edge from Miiller's monograph, instead of going to nature for 

 facts, the assumption being that Muller saw everything worth 

 knowing and saw it right. As illustrating the condition of our 

 knowledge of myxinoid anatomy at the present time we shall 

 cite the statements with reference to these animals in Parker 

 and Haswell's Text-Book of Zoology, which is perhaps the most 

 excellent zoological text -book in any language up to date. 



On page 115, under the head of the "Distinctive Characters 

 of the Craniata," it is stated that " the pharynx is of moderate 

 dimensions and is perforated by not more than seven pairs of 

 gills." In 1894 'Dr. Ayers called attention to the general 

 neglect, of which this is an example, of the fact that Bdellostoma 

 dombeyi has from 6 to 14 pairs of gills, and that consequently 

 in any statement of the general characters of the Craniata 

 such an important and evidently ancestral character must be 

 given prominent notice. Instead of this it has been generally 

 ignored. 



In the same paragraph it is stated that there are at least 

 ten pairs of cranial nerves, whereas in Bdellostoma we can 

 show that there is no trace of the three eye-muscle nerves. In 

 the description of "Class i — Cyclostomata " it is stated that 

 these animals are "distinguished from all other Craniata by 

 the possession of a suctorial mouth devoid of functional jaws, 

 by a single olfactory organ." In 1890 Dr. Ayers proved con- 

 clusively that the Petromyzontes had a pair of nasal organs, 

 and again, in 1894, that the myxinoids were no exception to 

 the general rule among the Craniata, since Bdellostoma and 

 Myxine possess a paired nasal organ. Dr. Ayers also showed 

 conclusively that the myxinoid mouth is not suctorial but 

 raptorial. 



With reference to the absence of functional jaws, we refer 

 to the following pages and plates, in which we believe we have 

 demonstrated that in these fishes the lower jaw is present and 

 functional, while the upper jaw is rudimentary and fused with 

 the cranial cartilages. With reference to the inaccuracies and 



