450 
MR. W. K. PARKER ON THE SKELETON 
is shown on each side ; the sinuosities of the bar cause it to be severed at many 
points,— six on each side. The enclosing bars, and the inbent form of the main 
bar behind the aperture, are well seen. 
1 7tli Section (Plate 26, fig. 13).—This is through the forepart of the myelon (my.), 
a curiously flat structure, convex above and concave below. This, which may be 
through the second or third pair of pouches, shows the thyroid body (th.) below. 
Under it the lower part of an extra-branchial (ex.br.) is cut across, and at the apertures 
the cross bars and part of the inbent main bar is seen. The theca vertebralis 
is much larger than is necessary for the myelon (my.), but it is not much greater in 
diameter than the notochord (nc.), with its thick membranous sheath. Under it we 
see the aorta (ao.), and outside it other large vessels. 
Summary and Conclusion. 
The remarks now to be made must be considered to be a continuation (with some 
repetition) of those given at the end of my 1st Part. 
These Fishes appear to have been given up in despair by most recent Anatomists, and 
yet Johann Muller laid a solid foundation for all his successors to build upon. 
Anyone may be proud to become a continuator of, and a commentator on, that great 
and almost unerring observer. 
A continuator and a commentator worthy of him has, from time to time, thrown light 
upon these types. I refer, of course, to Professor Huxley, whose researches, however, 
needed, what they have now to a great degree obtained, namely, the corroborating and 
also the correcting light derived from Embrology. Following in the footsteps of the 
lamented Ca leer la, Mr. W. B. Scott has done, and is still doing, excellent work in 
this way, but (before our great loss) Professor F. M. Balfour had shed most welcome 
light upon this subject. 
The problem of the morphology of this group has been to me for years an irritating 
opprobrium, on account of its apparent insolubility; and I have again and again made 
advances upon it, sideways, or crabwise, fresh from the contemplation of more normal 
types. Those Ichthyopsida that undergo metamorphoses after hatching, and thus 
have a larval stage during a longer or a shorter time, are of the most service in 
this matter. Hence I infer that the Marsipobranchs belong to a low grade, and that 
even supposing the Myxinoids to be degenerate descendants of some more developed 
form, yet I feel quite certain that such an archaic non-degenerate Myxinoid would lie 
far below our known existing Fishes, such as the Elasmobranchs, Ganoids, and Teleos- 
teans. But the three groups just mentioned lie far out of the way of the Marsipo¬ 
branchs. The early stages of the Anurous Batrachia give us the best clue to them, 
and far off as they are from them, they are indeed their nearest existing rela¬ 
tives. What the early stages of the “ Chimmroids ” and “ Dipnoi ” would show, 
it is impossible to say ; unfortunately, their early stages are not known.* With 
* See Note to p. 411. 
