Thilo’s memoir on »Die Umbildungen an den Gliedmaßen der Fische«. 171 
pleasure to forward to him of the 14 of March 1590 the book’, 
in which these investigations were published. 
In his »Litteraturverzeichnis« Dr. TurLo indeed briefly mentions 
(pag. 352) these investigations of mine. As by translating my words 
(with the exception of a single one) quite correctly in his quotations, 
he proves that he understands the Danish language, I am sorry to 
see that I must have been extremely unfortunate in my expressions, 
as the account which he gives of my investigations is rather wrong. 
It is therefore quite natural that Dr. TuıLo can have no high opinion 
of the accuracy of my investigations as may be gathered from the 
fact that he has not deigned to send me his memoir. 
As my opinion of the manner, in which these mechanisms 
operate, differs a good deal from that of Dr. Taro, it may perhaps 
be of some interest that the differences between our interpretations 
should present themselves somewhat more distinctly than appears 
from the account — perhaps rather short — given by Dr. Tuıro. 
Before I try to make plain these differences, omitting all references 
to the works of previous authors, for the search of which I must 
refer to my book, I beg Professor GEGENBAUR to accept my best 
thanks for the kindness he has shown me by opening his columns 
to these remarks. 
The most essential difference between Dr. TuıLo’s view and 
mine is due to my distinguishing between two kinds of faces: the 
articular faces, by means of which the rays articulate’, and the 
scouring faces, which are able to scour against each other while 
moving, thus stopping or checking the movement (and at the same 
time producing a sound), or, if brought into full contact which each 
other, before the movement takes place, prevent the movement from 
being effected. In the articular faces the bone is generally but not 
always covered with cartilage; this is never the case in the scouring 
faces, which are covered with an exceedingly thin periosteum very 
intimately connected with the bone. These faces show various 
sculptures: where they reach their highest development, they are 
smooth and, as it were, polished?”. On account of this fact I have 
1 WiLLIAM SORENSEN, Lydorganer hos Fiske. Kjébenhavn 1884. 
2 The word >articulate« being also used in English to express a connection 
f. i. between two bones which do not move against each other, I here take the 
liberty to remark that I use this word only when there is a real diarthrosis. 
3 As to the structure of the bone of the scouring faces I refer to my 
book, pag. 28—30. 
