64 
J. BEARD. 
Spencer (No. 14, PI. XVI, figs. 18 and 19). It appears to be 
more degenerate than that of Petromyzon, though hearing in 
mind the variability of the organ in the latter form we must 
not shut out the possibility that some Myxine may present a 
much better developed eye than that under description. 
In the one specimen of Bdellostoma at my disposal I could 
make nothing out of the structure of the organ ; however, as 
the brain of this form very closely resembles that of Myxine, 
as Johannes Muller 1 first showed, it is not at all unlikely that 
the resemblance will extend to the structnre of the parietal 
eye. The two forms, Myxine and Bdellostoma, are certainly 
very closely allied, and in other points of great importance, 
such as the structure of their teeth, they closely resemble each 
other and form a contrast to the Petromyzontidie, which while 
in some respects less degenerate than the former are in others 
less primitive. 
General Considerations and Conclusions. 
It was with the hope of getting at the phylogenv of this 
remarkable sense organ that I began researches on its develop- 
ment and its distribution in the group of Fishes. But indeed 
the result was only to find that the development explains very 
little. It is peculiarly one of those cases in which, as Dohrn 
so often insists, “ niclit Anfangs und Endpunkt das wahre 
phylogenetische Problem bilden, sondern der unbekannte Weg, 
der sie verbindet.” 
Leydig, whose misfortune it was to discover the organ in 
Reptiles years before the modern perfected methods of re- 
search enabled de Graaf and Spencer to convert Rabl-Riick- 
hard’s (No. 15) and Ahlborn’s theoretical conclusion into 
proved facts (No. 13, p. 535), has recently made use of 
his undoubted right to an opinion on the question, and 
declares his conviction 2 that the organ belongs to the system 
1 ‘ Vergleichcnde Anatomie der Myxinoiden,’ p. 176. 
2 From a former (erroneous) discovery of his that the organ in Batrachia 
is enncrvated by the trigeminus. There can be little doubt that this is 
wrong. 
