THE DEVELOPMENT OF THE MOUTH AND GILLS IN 
BDELLOSTOMA STOUTI. 
BY 
CHARLES R. STOCKARD. 
From the Zoological Laboratory, Columbia University. 
WitH 36 FIGURES. 
Eminent morphologists (Goette, 75, Huxley, 76, and W. K. Parker, 
83) have long since suggested the affinities of the Marsipobranchii and 
the larval amphibia, and Dohrn, 83, has even maintained that the 
cyclostomes are to be regarded as the descendants of highly organized 
fishes, possibly teleosts. Beard, 89, furthermore is of the opinion that, 
“While accepting some degeneration in the Marsipobranchs along with 
Dohrn, the truth of Balfour’s view that they are very primitive forms 
must also be allowed. They must undoubtedly be added to the gnatho- 
stomatous vertebrata. The Marsipobranchii stand between the selacians 
and ganoids, but far more related to the latter than to the former.” 
The view of Balfour, 85, here referred to held them to be degenerate but 
not derived from relatively highly organized fish,as is shown by his follow- 
ing words, “ Dohrn was the first to bring into prominence the degenerate 
character of the cyclostomata. I cannot, however, assent to his view 
that they are descended from a relatively highly-organized type of fish. 
It appears to me almost certain that they belong to a group of fishes in 
which a true skeleton of branchial bars had not become developed, the 
branchial skeleton they possess being simply an extra branchial system, 
while I see no reason to suppose that a true branchial skeleton has dis- 
appeared. If the primitive cyclostomata had not true branchial bars 
they could not have had jaws, because jaws are essentially developed 
from the mandibular branchial bar. These considerations which are sup- 
ported by numerous other features of their anatomy, such as the char- 
acter of the axial skeleton, the straightness of the intestinal tube, the 
presence of a subintestinal vein, etc., all tend to prove that these fish are 
remnants of a primitive and pregnathostomatous group. The few sur- 
viving members of the group probably owe their preservation to their 
parasitic or semiparasitic habits.” Whether Balfour’s reasoning regard- 
oe JOURNAL OF ANATOMY.—VOL. V. 
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