1024 KEPOKT OF COMMISSIONER OF FISH AND FISHERIES. [44] 



Balfour's theory aud against that of Gegeubaur-; but I am now in- 

 clined to think, in view of certain facts observed by Fiirbringer (Mor- 

 phologisches .lahrbuch, IX) as to the origin of the nerves supplying 

 the pelvic fin in some Teleosiei with thoracic or jugular pelvic tins, that 

 the portion of the spinal nerves from which the plexuses are derived is 

 too plastic a factor to support any wide generalization at all." At any 

 rate, the only way to settle this question now is to investigate some such 

 form as Lophius and trace the genesis of the innervation of the pelvic 

 lin by theembryological method, to see if the nerve supply of that fin is 

 derived from the segments with which its first rudiment w^as homono- 

 mous, or whether its nervous supply originates from segments in ad- 

 vance of those from which it was derived. There is, for obvious reasons, 

 little hope of settling this point by the method of comparative anatomy 

 or the comparison of the morphology of adult forms. 



Agassiz' figures also show that there are at most but four mj^otomes 

 interposed between the early rudiments of the pectoral and pelvic fins, 

 a number which is far less than in the case of the Salmon, where there 

 are about sixteen, or four times as many. We thus find that the tend- 

 ency to develop the pelvic fins is in some cases conspicuous at a very 

 early stage. In Gadus the rudiments of the thoracic pelvic fins evidently 

 do not appear until after the yelk is absorbed. Judging by the results of 

 my investigations on the early stages and those of Agassiz on the later 

 ones. In Moiella {Onos of Ay res) .the development of the pelvic fins is 

 about as nearly synchronous as in LopMusi according to Agassiz, and 

 the translocation forwards of the base of the pelvic fins probably occurs 

 in much the same way. 



In a larval pelagic form of Flounder from the Mediterranean, named 

 Feloria ruppelii^ by Cocco and studied by Emery,* the pectoral is re- 

 markably pedunculate before asymmetry begins to show itself, and the 

 ventrals are pushed forward in advance of the base of the former. The 

 four anterior rays of the dorsal are also free at the ends and much ex- 

 serted, a condition which appears to be evanescent, as in the case of 

 the young of Track ypterus. 



The embryological data so far acquired seem to indicate that the 

 rudiments of the pelvic fins of the embryos of forms with permanently 

 abdominal fins are not translocated forward during development, while 

 in those forms which have thoracic or jugular fins such a translocation 

 actually occurs. While nearly all of the Palaeozoic Ganoids had the 

 pelvic fins abdominal in position, some, us Blochius, for example (if that 

 form is really a Ganoid), had them almost jugular, which would seem to 

 indicate that such a translocation of the pelvic limb occurred relatively 

 late in the history of the evolution of the fishes. The Physostomi also 

 being the most primitive type of Teleosts, have mostly retained the pel- 

 vic fins in the archaic abdominal position, whereas the more highly 



* Contrib. all" ittiologijj,. Reale Accad. dei Lincei. Classe di scieiizetisichej ruatb. o 

 uaturali, XIV, 1883. 



