Thilo’s memoir on »Die Umbildungen an den Gliedmaßen der Fische«. 177 
same thing may also happen when you carıy forward the spine; 
but then the faces are not sure to remain in the same position when 
the spine is again carried backwards.) 
What turns out to be the most decisive proof is this: When the 
scouring faces are brought into full contact with each other, in a 
specimen preserved in weak spirits of wine, or still better, in a 
recently! killed specimen, then it is impossible to carry the spine 
backwards from an erect position, no matter whether you try to do 
so with your hand or by pulling at the muscles p?. If the specimen 
has a slender spine, or if it is in a bad state of preservation, you 
may in your attempt break the spine or tear asunder the ligament 
between the rays I and II. But it is impossible to move the spine 
(when quite erect) backwards, when those faces which Dr. Taito 
considers as articular faces are brought into full contact with each 
other. 
After having set forth my interpretation of this mechanism and 
accounted for it, I beg the reader to peruse attentively what Dr. 
THILO writes on this subject with regard to Synodontis (pag. 309— 
317) and then see, whether be can understand that this author gives 
any explanation whatever of the fact that the rudimentary ray is 
subject to fixation. 
The pectoral fins of the Siluroide. (My book, pag. 20—50.) 
The pectoral fin I had examined in the genera: Doras, Syno- 
dontis, Euanemus, Pseudaroides, Clarias, Platystoma, and Silurus 
(and with regard to the skeletal parts, Plecostomus). Both the size 
and the effect of the muscles, the form and the size of the process 0, 
acting as a brake, and its scouring faces with their surfaces, and 
partly the form of the diarthrosis vary in these genera. To be 
brief I will confine myself to give a short statement of the structures 
in Doras and Synodontis, while for the more detailed description I 
refer to my book. I must remark that in Doras and Synodontis 
the structures are the same on all essential points, with the only 
exception that, unlike that of Doras, the process ö in Synodontis 
has both faces naked i. e. scouring all over, though at the same time 
they present smoother parts towards the fore- and hindend, consi- 
! I myself have not examined such specimens of Synodontis but several 
of Doras and Pseudaroides (as well as Platystoma). 
12* 
