[33] THE EVOLUTION OF THE FINS OF FISHES. 1013 



forms are probably suppressed axial segments of tbe limbs, which were 

 probably functional in tbe limbs of lower forms. This view is further 

 sustained by the fact that there is a tendency toward synostosis of 

 many other elements of the skeleton in the higher forms, whereas their 

 homologues in the lower ones remain distinct through life. In the light 

 of such embryological research it will also become less difficult to under- 

 stand the i30ssible origin of a manus with more than three phalanges 

 in each digit, as found in some Cetacea, of the development of which 

 we know little or nothing relating to the bones of the limbs. 



VI. — On the protopterygian stage of development of the 



RAYS IN THE FINS. 



As stated in another portion of this paper, it was proposed to dis- 

 criminate a so-called lophocercal stage following that designated as the 

 archicercal and characterized by the want of tin-rays as understood in 

 speaking of the adult condition. A very remarkable kind of rays are, 

 however, developed during the lophocercal stage of Teleosts which be- 

 come most clearly marked just at its close, or when the permanent tins 

 are about to be developed. These emhryonic fin-rays * as A. Agassiz has 

 called them, were observed by C. Vogt about 1840 (and are alluded 

 to) in his essay entitled Emhryologie des Salmones, but they were posi- 

 tively shown to be connected with the formation of the permanent rays 

 about twenty years since by Theophile Lotzt in a paper not devoted to 

 the rays themselves, and the fact has therefore been apparently over- 

 looked that to this author properly belongs the credit of -having first 

 pointed out that the filamentous embryonic rays stand in a genetic 

 relation to the permanent rays which are derived from them. A. 

 Agassiz nowhere in his several papers intimates that such a relation 

 exists between the embryonic and permanent rays, although he has 

 found the former in a great mauj^ genera of osseous fishes besides those 

 in which they have been found by the writer, so that it seems probable 

 that such rays will be found in the embryos of all Teleostei. Lotz found 

 them in the young Salmon just after hatching immediately underlying 

 the larval integument of that part of the median fin-fold which is des- 

 tined to become the permanent caudal, but he says nothing of their more 

 extensive distribution iu other fins. It now remains forme to state (1) 

 that these rays are first develo^jed just beneath the epidermis of the tin- 

 fold, Fig. 9, PI. IX; (2) that there are two series, one»uuder the right 

 and the other under the left epidermic wall of the fold with some me- 

 soblast insinuated between the two series, Figs. 4, 5, 6, and 7, PI. IX; (3) 

 they are, as pointed out by Lotz and Agassiz, very much more numerous 



* Since this has gone to press the necessity of giving these elements a single name 

 has become manifest to me, and iu a later paper I have therefore named them actiri- 

 oirichia. 



tUberdeu Bau der Schwanzwirbelstiule der Salmoniden, Cyprinoiden, Porcoiden 

 uud Cataphracteu. Zeitschr. wiss. Zool., XIV, 2. Hft., 1864. 



