Morphological Studies. 743 



The oi-der of degeneration, taking the most degenerate forms first, 

 as above, is identical with that one can deduce from the teeth. 



For other reasons it is especially interesting and important that 

 the Myxinoids should present more primitive conditions than the Petro- 

 myzontidae. The identification of the oral hypophysis as the remains 

 of the old Vertebrate mouth depends on that point, and it is hence 

 very satisfactory to find there is evidence, stronger than any yet ad- 

 duced, for the older and more primitive nature of the Myxinoids. It 

 should not be forgotten that Profs. Huxley (12, p. 428) and W. K. 

 Parker have already expressed themselves in this sense. 



What the relations of the group to other fishes are shall now be 

 examined, and, as far as possible, the question be answered: — are 

 the Marsipobranchii degenerate, or primitive fishes, or both? 



According to Prof. Haeckel (9, p. 425) they „sind von den 

 Fischen weiter entfernt als die Fische vom Menschen. Wir müssen 

 sie daher als die letzten Ueberbleibsel einer sehr alten und sehr tief 

 stehenden W irbelthierklasse betrachten, welche noch lange nicht die 

 Organisationshöhe eines wirklichen echten Fisches erreicht hatte". 

 At the same time he regards the sucking mouth as a secondary ad- 

 aptation, and in this respect he differs, as we shall see, from Prof. 

 Balfour. 



Gegenbaur (8, p. 409) speaks with much more caution about the 

 position of the group, and maintains that „the Cyclostomata should be 

 placed apart from the rest of the Craniota, for their whole organi- 

 sation shows that they branched ofi" very early from the Craniota". 



Wiedersheim (23, p. 126) also expresses himself with reserve 

 on the matter, but is rather disposed to accept, at any rate partially, 

 Huxley's comparison of the cranial skeleton of Petromyzon with the 

 larval amphibian skull. 



He writes (p. 126) : „Die isolirte Stellung der Cyclostomen macht 

 es sehr schwierig, diese Fischgruppe in irgend welche genetische Be- 

 ziehung zu anderen Wirbelthieren zu bringen, und alle darauf gerich- 

 teten Speculatiouen müssen vor der Hand als sehr gewagt be- 

 zeichnet werden. Gleichwohl will ich nicht unerwähnt lassen, dass 

 gewisse Entwicklungsstadien der ungeschw^änzten Batrachier auffallende 

 Aehnlichkeit mit dem Schädel des Ammocoetes besitzen, so dass man 

 vielleicht beide als aus einer gemeinsamen Stammform entsprungen 

 betrachten darf (Huxley)." 



Prof. Huxley (12, p. 412 et seq.), like Balfour and Dohrn, 

 took up a much more decided position, and showed that in the skull 



