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Raymond C. Osburn 1 
XI. Collector nerves and plexuses are known to occur commonly in 
both paired and unpaired fins, and, though usually more marked in the 
anterior margin of the fin, they are of frequent occurrence in the pos- 
terior as well. (For the paired fins, Davidoff, 79; Mollier, 93; Punnett, 
00, or; Braus, 98, oga; for the unpaired fins, P. Mayer, 86; Good- 
rich, 06.) 
XII. The bases of the paired fins and of the dorsal and anal fins be- 
come concentrated during development. (Mayer, 86; Mollier, 93; Good- 
rich, 06.) This is least marked in the case of the caudal fin and most 
marked in the pectoral fins, and between these extremes there exist all 
intergradations in anal, dorsals, and pelvics. Measurements show that 
the base of the pelvic fin of Chlamydoselachus is comparatively longer 
than that of the dorsal fins of Cestracion or Spinax. 
XIII. All types of fins may migrate or be displaced during develop- 
ment. Such migration is always of shght degree, though often meas- 
urable, and.may be in either direction (Dean, 02; Punnett, 04). 
XIV. Ceratotrichia, or horny rays of the fins, develop in both paired 
and unpaired limbs and occur in no other part of the body. They are 
equally ancient in either type of fin (Goodrich, 03; Osburn, o6b), and 
appear at about the same time in ontogeny (Goodrich, 03). 
The foregoing points may be considered as already decided. Upon the 
points which are still under consideration, the writer desires to present 
the following data and discussion: 
Fuston or Muscie-Bups. 
Muscle-buds may fuse during their early development in the unpaired 
as well as in the paired fins. Such fusion or blending was first de- 
scribed and figured in the pectoral of Torpedo by Mollier, 93. Later, 
Fiirbringer, 02, and Braus, oga, used this fact, in opposition to the fin- 
fold theory, as evidence against the metamerism of the adult muscles of 
the paired fins, and so, also, of the corresponding skeletal rays. My 
own work on Cestracion, however, shows that fusion of muscle-buds is 
not confined to the paired fins, but, on the contrary, may occur in any of 
the unpaired fins. Hence, as I have already indicated, o6b, any argu- 
ment against the fin-fold theory based on such ground is altogether 
futile. In Cestracion fusions were found in all of the unpaired fins,— 
even in the caudal, though more sparingly here——and the nature of the 
blending is exactly similar to that in the paired fins. Fig. 17 shows 
such a fusion in the anal fin of a 35 mm. Cestracion embryo. A com- 
parison with Mollier’s figure (93, Taf. III, Fig. 15) of this condition in 
