Thilo’s memoir on »Die Umbildungen an den Gliedmaßen der Fische«. 175 
kein Kegelgelenk«, then this is quite correct. But when he con- 
tinues: »und der Gelenkkörper [d, in my Fig. 1], welchem der 
Strahl 1 aufliege, könne kein Doppelkegel sein«, then, I suppose, 
I have not been fortunate enough to express myself distinetly: in 
Synodontis (but not in all Siluroide) the roof-like keel 0 may 
very well be called a »Doppelkegel« (though its faces are doubly 
curved); what I had said is, on the contrary, that this »Doppel- 
kegel« is not a Gelenkkörper. — What he quotes from me is correct, 
but his preceding »denn« is misleading!. For I said this in order 
to illustrate my remark that I was of opinion that he ought not to 
have stopped at »diese auf den ersten Blick wohl nicht ganz ein- 
leuchtende Behauptung«. — When he says: »Welche Gelenkform 
er annimmt, giebt er nicht an, sondern spricht an dieser und an- 
deren Stellen nur von ‚glatt polirten, nackten Flächen‘, wenn von 
Gelenken die Rede ist. Angaben der Gelenkformen und Gelenk- 
achsen fehlen«, then this too must, I suppose, be owing to my having 
been unfortunate enough not to express myself with sufficient di- 
stinetness. I had said pag. 10 that the diarthrosis of the rudimentary 
ray is a gliding joint; and pag. 12—13 I wrote: »By a glance at 
the Figg. 2—4 [in my book] it will easily be seen that, as for the 
rudimentary ray, this movement follows a circular line (backwards 
and upwards), the centre of which is the diarthrosis of the spine.« 
This diarthrosis, consisting of three articular faces, I had described 
pag. 11 and said: >»... so that the spine cannot be moved sideways«. 
And, »wenn von Gelenken? die Rede ist«, I had never mentioned 
»glatt polirten, nackten Flächen«, though Dr. Tuo tells so. — 
When Dr. Tuıto’s says: »Auf meine Messungen und Bestimmungen 
der Gelenke [i. e. the scouring faces in Synodontis|, die ich... 
vornahm, geht er [I] nicht ein«, then this is quite correct. The 
reason why, neither in Synodontis nor in any of the other genera 
of the Siluroide I have cared to measure the angles, was the 
following: the angle between the scouring faces is different in the 
different genera, and in Platystoma the roof-like keel is rounded, 
its faces accordingly form no angle; on the whole it may be said 
1 Dr. THILO says: >»... der Gelenkkörper ... könne kein Doppelkegel 
sein, denn ‚im Fußgelenk des Pferdes giebt es sogar zwei solche (Doppelkegel) 
am Astragalus, doch hat gewiss Niemand gedacht, dass die Beweglichkeit durch 
diese sollte aufgehoben werden können‘.< 
? The italics in this and other quotations are mine. 
Morpholog. Jahrbuch. 25. 12 
