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indicated by the above title. I am aware that almost every writer on 
Marsipobranch morphology has availed himself of the opportunity of 
saying something upon this subject and yet it appears to me, on the 
one hand, that the significance of certain anatomical facts has not 
been properly, if at all, appreciated, and, on the other hand, that 
certain arguments employed by some recent authors are extremely 
fallacious. Since the relatively lengthy summary of my arguments 
which appears in the Report of the Portsmouth meeting of the British 
Association is yet all too brief for their suitable presentation, I think 
it as well to publish these arguments in extenso now that three 
months’ relaxation from my official duties provides me with the op- 
portunity. 
It is evident that all hypotheses concerning the supposed affinities 
of the Marsipobranchs with particular Gnathostome groups (e. g. those 
of Gore, 16, Huxrey, 21, PARKER, 28 and Doury, 9) imply a 
Gnathostome ancestry for the Marsipobranchs, and of late years this 
assumption of Gnathostome ancestry has gained considerable acceptance 
owing to the publications of AyERS and JACKSON (3), STOCKARD (37) 
and others. Since, on the other hand, this view has been opposed in 
the past by such authorities as HaEckEL (18), BALFOUR (4), Howes 
(20) and Max FÜRBRINGER (10, 11), whilst other authorities—e. g. 
BASHFORD DEAN (7), CoLE (6), GooDricH (15)—continue to maintain 
a more or less agnostic attitude, it seems worth while to enquire into 
the validity of the additional evidence advanced in support of the 
theory that the ancestors of the Marsipobranchs were jaw-bearing 
Craniates and if possible to arrive at some definite conclusion. 
I may first of all state that it is not my intention to discuss in 
detail the views of those authors who in the past have endeavoured 
to piece together and reconstruct from the head cartilages of the 
Marsipobranch the jaw and hyoid arches of the Gnathostome. Even 
if it be granted that the innervation, musculature and relationships 
to adjacent tissues and organs collectively prove that the posterior 
half of the subocular arch, the posterior lateral cartilages and the 
median ventral are homologous with certain parts of the mandibular 
arch, or that certain other cartilages represent displaced deformed 
portions of the hyoid arch, yet these facts do not constitute grounds 
for supposing that jaw and hyoid arches of the Gnathostome type ever 
existed in the Marsipobranchs. Because the fins of fishes are homolo- 
gous with the limbs of Tetrapoda we do not therefore of necessity 
