XXV 



indebted to the labors of Agassiz, Liitken 1 (see p. x), Cope (see p. x), 

 and Lankester. 



THE GANOIDS A NATURAL GROUP. 



It has been objected that the Ganoids do not constitute a natural group, 

 and that the characters (i. e., chiasraa of optic nerves and multi valvular 

 bulbus arteriosus) alleged by Miiller to be peculiar to the teleostomous 

 forms combined therein, are problematical, and only inferentially supposed 

 to be common to the extinct Ganoids so called, and, finally, such objections 

 couched in too strong language have culminated in the assertion that the 

 characters in question are actually shared by other physostome fishes. 



No demonstration, however, has been presented as yet that any physos 

 tome fishes do really have the optic chiasma and multivalvular bulbus ar 

 teriosus, and the statement to the contrary seems to have been the result 

 of a venial misapprehension of Prof. Kner s statements, or the offspring of 

 impressions left on the memory by his assertions, in forgetfulness of his 

 exact words. 



But Prof. Kner, 3 in respect to the anatomical characters referred to, 

 merely objects ; (1) they are problematical, are not confirmable for the 

 extinct types, and were probably not existent in certain forms that have 

 been referred to the Ganoids ; (2) the difference in number of the valves 

 of the bulbus arteriosus among recent Ganoids is so great as to show the 

 unreliability of the character ; (8) a spiral valve is developed in the intes 

 tine of several osseous fishes (&quot; genera of the so-called intermediate clu- 

 peoid groups&quot;) as well as in Ganoids ; and (4) the chiasma of the optic 

 nerves in no wise furnishes a positive character for the Ganoids. 8 



1 The extended memoir of Dr. Liitken (Om Ganoidernes Begraendsning og Inddel- 

 ing) contains a valuable resume of the history, up to 1867, of the Ganoids, as well as 

 a full bibliography relating to the group, and a critical discussion of the forms re 

 ferred to it. 



2 KNER (Rudolph). Betrachtungen iiber die Gano iden, etc. &amp;lt; op. cit. (supra, p. 

 00), p. 522. 



&quot; Noch andere der angefiihrten Merkmale sind geradezu problematisck, da sie nur 

 auf rnuthmasslichen Voraussetzungen und Aunahmen beruhen, nicht aber als 

 wirklich vorhanden nachzuweisen sind. Zu solchen gehoren die von J. Muller fur 

 lebende Ganoiden hervorgehobenen anatomischen Merkmale: [1] der muskulose 

 Bulbus mit mehreren Klappenreihen, [2] das Chiasma und [3] die Spiralklappe im 

 Darmcanal. . 



[1] Fiir die allermeisten fossilen Fische, die fur Ganoiden gelten, ist nicht nachweisbar, 

 dass diese Merkmale vorhanden waren und vielmehr mit Grund zu vermuthen, dass 

 sie namentlich solchen nicht zukamen, die in alter Zeit als Protypen spiiterer Teleo- 

 stier auftreten,&quot;wie z. B. den triasichen Gattungen Belonorhynchus, Pholidophorus u.v.a. 

 Allein ganz abgesehen hievon, so durfte doch darauf hinzuweisen sein, in welch un- 

 gleichein Grade sich diese Merkmale selbst bei den verschiedenen Gattungen der le- 



