FINS or GANOIDS AND TELEOSTS. 



589 



the character of the radial elements of different portions of the 

 dorsal fin in these families may be represented in the following 

 Table, 



Name of Species, 



Number of 



radial 

 elements. 



Trisegmental. 



Bisegmental. 



Unisegmental. 



Esocidse. 



20 



10 



22 



12 



6-15 



5-9 

 3-21 



6-11 



2-5, 16-20 



1-2 

 3-5 



1 



10 



22 



1-2, 12 



OyprinidEe. 



£arbus vulgaris ... 



Cyprinus carpio . . . 

 Salmoaidse. 



Coregonus foUan . . . 



Tiie existence of trisegmental radial elements in Teleosts has 

 not previously been recorded, at all events so far as I have been 

 able to discover. The development of the radial elements has 

 been studied by Harrison [3] ; and from the results of his 

 investigations in Salmo salar and Carassius auratus it would 

 appear that each element first makes its appearance in the form 

 of a somewhat curved cartilaginous rod or " Flossenstrahltrager," 

 the convexity of which is directed forwards. " Schliesslich bildet 

 sich aus dem undifferenzirten G-ewebe am Ende jedes "Plossen- 

 strahltragers ein kleiner kugelformiger Knorpel, mit dem sich 

 der Flossenstrahl eng verbindet. Jedes Flossenstrahlpaar um- 

 greift die knorpelige Kugel mit ihrem centrale Eude, welches 

 zu einem kurzen und beinahe horizontalen Fortsatz umgebogen 

 ist, und zwei Grebilde vereinigen sich vollstandig vermittelst 

 eines starken Bindegewebes " (Z. c. p. 521). No mention is made 

 of mesial segments, although such segments are undoubtedly 

 present in both the Salmonidse and Cyprinidse in the adult state, 

 but it is probable that the omission is due to the fact that 

 Harrison's investigations were principally directed to the origin 

 and metameric relations of the fin-muscles, and ceased at a much 

 earlier stage than that at which the radial elements attain their 

 adult characters. As regards the origin of the mesial segments, 

 two alternative methods may be suggested. It is of course 

 possible that, like the distal segments, they owe their forma- 

 tion to the chondrification of indifi"ereut connective tissue 

 between the " Flossenstrahltrager " and the cartilaginous nodule 

 representing the distal segment at a later stage ; or it may be 



