316 General Notes. [ March, 
tween the pelvic and pectoral fin-folds, whereas in the young 
salmon, relatively somewhat older, there are at least sixteen myo- 
tomes opposite the interval between the pelvic and pectoral fin- 
folds. This fact would seem to indicate that the tendency to shift 
the pelvic limb forwards must have commenced to manifest itself 
far back in the ancestral history of Lophius. 
The sudden translocation of the pelvic fin of Lophius, which 
now follows in the next stage figured by Agassiz, gives us a clear 
conception of how the jugular or thoracic position of the pelvic 
_limbs of Physoclists has been brought about. It also clears away 
the difficulties which Haswell and Fiirbringer have encountered 
in reconciling the condition of the nerve supply of such shifted fins 
with the theory of the origin of the paired limbs from continuous 
folds or serially homologous rudiments, as developed by Balfour 
and Dohrn. For, in the next stage, we find the base of the pelvic 
fin suddenly swung round, down and forward through an arc of 
nearly 90°, so as to carry the whole structure below the base of 
the pectoral. This shifting is then carried still further, so that 
the bases of the pelvic fins are finally situated below and in front 
of the insertion of the bases of the pectorals. The other equally 
singular and extraordinary embryonic changes undergone by 
Lophius we cannot discuss at present, but would refer the reader 
to the original memoir. 
This remarkably sudden shifting of the pelvic fins of Lophius 
embryos, within a period of twenty-four hours, is a fine example 
of saltatory development, or of how a sudden developmental 
leap may be manifested, which does not very seriously involve 
adjacent structures. Embryonic development is, in fact, every- 
where diverted from its archetypal mode, so to speak, by such 
interference with the primordial synchrony or primitive order in 
time and space of the appearance of different organs. It is the 
business of the philosophical morphologist to keep in mind the 
import of such phenomena, and to weigh their significance in the 
discussion of the evolution of organic forms, 
he nerves, vessels, muscles and bones appertaining to the suc- 
cessive rays of the median fins are, as is well known, derived from 
embryonic metameres which are simply more developed or dif- 
ferentiated in the adult. The cartilaginous rays or actinophores* 
of the paired fins of the Elasmobranchs and the rays of the un- 
paired fins of Teleosts are known to sustain such a relation of 
~ homonomy to the primary metameres first indicated in the em- 
ae bryo, though in some types two, three or even five actinophores 
~ may stand in a derivative relation to such a single embryonic 
‘Segment or somite. There is also much ground for the belief that 
in the paired fins of Teleosts it is possible to trace such a relation 
_ between the somites over which they originally arose and the 
_actinosts or actinophores which constitute their axial skeletons, 
: ae skeletal elements which afford support to the true fin-rays 
