170 



Our knowledge of the structure of the teeth of Cyclostoniata is 

 entirely confined to the observations of J. Müller, F. E. Schultze, 

 Langerhanh, W. K. Parker and Tomes. So far as I am aware no 

 other author has investigated the matter, but my friend and teacher 

 Prof. Howes informs me that the curious structure of the true horny 

 teeth of Petromyzon marinus described below has long been known 

 to him. 



J. Müller^) descriljed the teeth of all the members of the group 

 as horny, and concerned himself solely with their arrangement in 

 the mouth. 



F. E. Schultze ^) gave the first detailed account of the minute 

 structure of the simple horny plates in P. fluviatilis, showing that 

 they rest on a slight dermal papilla and that they fit into special 

 epidermal depressions at the base of the papilla. 



Langerhans ^) in a paper which is unfortunately buried in one of the 

 older volumes of the Verhandlungen der Naturforschenden Gesellschaft 

 zu Freiburg i. Br, could do nothing more then confirm Schultz e's 

 account. Tomes*) in his book on the teeth of Vertebrates only speaks 

 of the horny teeth of the Cyclostomata and points out how entirely 

 different they are from the teeth of the rest of the Vertebrata. 



Parker-'') in his beautiful monograph of the development of the 

 skull in Marsipobranch fishes mentions the bright yellow horny teeth 

 of the Myxinoids. 



So far as P. fluviatilis vel planeri is concerned I can but confirm 

 the accounts of my predecessors, and will only add that the horn 

 appears to arise in the special basal epithelial grooves. 



In Petromyzon marinus though the essential structure is the same 

 as in the fi*esh water form, a greater complication occurs in that not 



1) J. MtJUEK, Anatomie der Myxinoiden, p. 84. 



2) F. E. ScHTJLTZE : Über Cuticularbildungen und Verhornung von 

 Epithelzellen bei den Wirbeltieren. Archiv für mikrosk. Anat. Bd. V, 

 p. 310, Taf. XVII, Fig. 10. 



3) Paul Langebhans, Untersuchungen über Petromyzon Planeri. 

 Verhandl. der Naturforsch. Gesellschaft zu Freiburg i. Br. Bd. VI, p. 39. 

 I commend this valuable paper of Langerhans to the notice of those who 

 say the sense organs of the lateral line in Petromyzon ,,are scattered and 

 without segmental arrangement" and that there is „no regular lateral line". 



4) C. S. Tomes, Anatomie der Zähne etc. German translation, 1877, 

 p. 153. 



5) W. K. Paekee: On the skeleton of the Marsipobranch j&shes. 

 Part I. The Myxinoids. Phil. Trans, of the Royal Society, Part II, 

 1883, p. 398. 



