Thilo’s memoir on »Die Umbildungen an den Gliedmaßen der Fische«. 179 
is pressed somewhat harder into the groove!. In this position the 
ray may be carried backwards by the muscle inserted on zp (or by 
the human hand) but cannot be carried forwards by the muscles 
inserted in the groove ea. — sp, the place of insertion of a small 
muscle, M. specialis?, which has an effect quite contrary to that of 
the muscle inserted on ep: the denticulated posterior edge of the 
ray is twisted a little upwards, the process 0 is twisted forwards 
and inwards, so that its interior face behind and its exterior face 
in front are brought into contact with the walls of the groove in 
»Humerus«. In this position the ray can be carried forwards by the 
muscles inserted in the groove ea, but not carried backwards by 
the muscle inserted on :p°. 
Now the investigations of Dr. TuıLo differ from what is stated 
here on the following points: 
a) While the figg. 26, 27, and 28 in my book, which represent 
the very muscles of Synodontis, show the above-mentioned 5 muscles, 
Dr. TuıLo only mentions 3; it is true, he has seen the 4 muscles 
normal to the rays of the pectoral fins in general, but the two muscles 
inserted in the groove ea appearing to him to be furnished with 
»eine gemeinschaftliche Sehne« (this, however, they are not) he has 
only counted these two muscles as one. 
b) Dr. Tutto has understood that, in order to carry the ray 
backwards (with the hand) it is necessary to give the ray a twist, 
viz. the torsion which is executed by the muscle inserted on ep. 
But he has not seen that, in order to carry the ray forwards‘, it 
! This groove in Doras and Synodontis has a diameter very little larger 
than that of the process J. 
2 This muscle which does only exist in Doras and Synodontis is a spe- 
cialised portion of the M. interior anterior. 
3 Though I want to speak as briefly as possible, I ought, however, to 
remark, that the muscle inserted on zp, in Doras and Synodontis also carries 
the back end of the ray a very little inwards, counteracting as for this part 
of its action the muscle inserted on ep, the process d is moved in the groove 
of >Humerus<, without scouring against the walls of the groove. Mutatis mu- 
tandis the same observation may be applied to the muscles inserted on ea with 
regard to the muscle inserted on sp (see my book, pag. 38—39). 
4 That this is the case, Dr. TuıLo might have learned not only from my 
book, but also from a paper by Duross& (in: Annales d. sci. nat. 5 Ser. T. XX. 
Paris 1874. Art. No. 3) to which I had repeatedly referred in my book. Duross& 
Says, pag. 120: »Tant que le Poisson a toute sa vigueur, il rend aussi souvent le 
bruit en étendant son rayon qu’en le rapprochant de son corps; mais des qu’il 
Saffaiblit, ce n'est durant l'abduction qu'il produit ce son incommensurable, et 
