BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. 147 
In all these points they differ from the Seitenorgane of the 
Capitellidz and, interesting and important as Hisig’s researches 
are, we must at present, I think, hesitate to accept the pro- 
posed homology. 
PHYSIOLOGY OF THE BRANCHIAL SENSE ORGANS. 
Of this we really know nothing. Leydig, who has the honour 
of having first described these sense organs, thought they were 
organs of a sixth sense. By others they have been regarded 
as touch organs, and as organs for testing the water breathed. 
Lastly, Mayser’ suggested that they were a low form of audi- 
tory organ, and Emery’ instituted a comparison between the 
auditory labyrinth and branchial sense organs, and concludes 
that the two sets of organs have an analogous function. That 
this is the case seems now very possible ; that they are concerned 
in the perception of wave motion is obvious enough from their 
structure. 
I have here shown, and Professor Froriep® has also come to 
the same conclusion, that they are the special sense organs of 
the gill-clefts. On this view we may assume that they give 
notice of impending danger to the gill clefts, and so enable the 
latter to be closed. Of course they were existent long before 
an operculum was developed in any fish. 
After this demonstration that these sense organs stand in 
some important relationship to the gill-clefts, it may reasonably 
be ‘expected that experimental evidence of their real nature 
will shortly be forthcoming. Here a valuable field of research 
is open for the physiologist, and a very important one too, for 
researches in it may lead to a better knowledge of other Verte- 
brate sense organs, such as the nose and ear, which appear to 
have been primitively of the same nature as these branchial 
sense organs. 
If the researches recorded here should give any impulse to 
1 Mayser, “Studien iiber das Gehirn der Knochenfische, ‘Zeit. f. Wiss. 
Zool.,’ vol. xxxvii, 1881. 
2 Emery, “ Fierasfer,” p. 48, ‘Fauna and Flora of the Bay of Naples.’ 
3 This was stated by Professor Froriep aud myself independently. 
