234 J. K. TJiacher — Ventral Fins of Ganoids. 



There is represented in fig-, i a peculiar foramen, which either did 

 not exist or was overlooked in the specimen figured in fig. 64. This 

 lono; tunnel enters the substance of the cartilage from the dorsal side 

 at the place marked/* and running in the middle of the cartilage, it 

 pursues the coiirse marked by the dotted line to emerge between the 

 rays 2 and 3. 



Its remarkable position, boring the substance of the cartilage to no 

 purpose, and the still more remarkable parallelism between its course 

 and the line of division between rays 3 and 4, are sufficient reasons 

 for regarding it as an indication of an early separation between these 

 two rods 2 and 3. The second foramen </ proceeds almost directly 

 through the cartilage. 



Now if we construct a fin in which all the rays are separate which 

 are separate in either of the two fins figured, and in which the sepa- 

 ration between 2 and 3, which is indicated in the way just spoken of, 

 is retained, we shall have a form of fin represented in PI. I, fig. 2. 

 From evidence then obtained wdthin the limits of this single species, 

 it is proved that there must have been fins of this form possessed by 

 some of the ancestors of these individuals ; fins in which each of the 

 eight simple rays maintained its independence and simplicity, except 

 so far as regards the concrescence of the proximal segments 1 and 2, 

 and the process a rising from the orad side of the first ray. 



Scaphirhynchns, as is well known, is the nearest living relative of 

 Aeipenser, and the two are very similar to one another. The dorsal 

 side of a left ventral of this fish is exhibited in PI. II, fig. 7. We 

 have here seven rays, but the orad one is so wide as to raise the 

 belief that it has been formed by the lanion of two. In this the betip- 

 ping fails. There is the same iliac process a growing up from the 

 edge of the fin, but the chief difference lies in the prolongation of the 

 pubic part,* and the degree of concrescence, which is greater than it 

 is in either of the specimens of Acipenser described. As is evident, 

 this fin throws no light on the general question here under discussion. 

 It is a mere modification of the Acipenser fin. And to this we return. 



We had arrived at a form, PI. I, fig. 2, consisting of eight simple 

 parallel rays, except that the two orad rays have united in their 

 proximal joints, and that there is the iliac process a, and that the 



* In the figure (PI. II, fig. 7,) the pubic part, which bends a little ventrad when in 

 position, is here flattened out and not foresliortened. It should be noted that the 

 aborad ray, 7, lies dorsad of the next ray, thus partially concealing it in the figure. 

 This is what we find as a general rule in the ventrals of Elasmobranchs, and the con- 

 formation is important in building the intromittent organs of the males. 



