188 William Sörensen 
Magen mit athmosphärischer Luft. 2) Er lässt von dieser Luft immer 
nur ganz geringe Mengen in das Wasser strömen, welches seine 
Mundhöhle ausfüllt. 3) Diesem Mundhöhlenwasser entnehmen die 
Kiemen den Sauerstoff und führen ihn so dem Blute zu.«< What 
then were his reasons to reject the investigations made already 
in the year 1808 by Erman on Cobitis fossilis according to which 
the air is expelled through the Anus after being respired in the 
intestinal canal; the investigations of JoBERT in 1877—1878, accord- 
ing to which the air, after being respired in the intestinal canal, is 
expelled either through the mouth or the anus in some species of the 
Siluroid genera Loricaria, Hypostomus, Callichthys, and Doras; and 
the investigations of Fr. Day in 1876—1877, according to which 
the air is expelled through the mouth after being respired in the 
accessory gill-cavity in the Siluroid genera Clarias and Saccobranchus ? 
2. As an »Ergebnis meiner [his] Untersuchungen« Dr. THILO says 
(pag. 349): »Die erweiterte Speiseröhre! der Gymnodonten kann, ver- 
gleichend anatomisch, als eine unentwickelte Schwimmblase betrachtet 
werden.« How then is the well-developed air-bladder in most of 
these fishes to be considered ? 
3. How can it (pag. 349) be called an »Ergebnis meiner [his] 
Untersuchungen« that the spines in fishes are »Gehwerkzeuge«, when 
in mentioning this thing Dr. TuıLo only refers to the observations 
of other authors? 
4. How can it (pag. 349) be called an »Ergebnis meiner [his] 
Untersuchungen« that the spines are »Lautorgane«, when in no fish 
whatever he mentioned any sound produced by means of the rays? 
5. Has it not been a weli known fact before his examinations 
appeared, that the spines in fishes are »Waffen« (pag. 349) ? 
6. Pag. 335 he says: »Bisher best man nur zu oft: ‚Die 
Schwimmblase kann nur ein Lautorgan sein‘, oder ‚sie ist ausschließ- 
lich Athmungsorgan‘ ete.< On account of my book, the largest sec- 
tion of which treats the air-bladder as a sound-produeing organ, I 
had studied as much of the literature on the air-bladder as I could 
manage and nowhere had I quoted any such statement in my book, 
in which I imagined I had pointed out that the air-bladder is a 
sound-produeing organ in a much greater number of fishes than 
! According to my paper »Om Oppustningssekken hos Tetrodon« (Natur- 
hist. Tidsskr. 3R. Vol. XIII. Kjöbenhavn 1883. pag. 379—396) the subcutaneous 
sac is not connected with the oesophagus but opens, as well in Diodon as in 
Tetrodon, behind in the pharynx. 
