IS ON THE APPENDICES GENITALES 1CLASPERS1 IN THE SELACHIANS. 



the ventral side of the fin, tinder the skin, but in the Holocep hales, where it has only been little 

 developed, limited to the appendix-shaft. 



The skeleton of the appendage belongs always to the axial stem of the fin-skeleton 1 ); among 

 the rays (in the PI agiostomes, not in the Holoeephales) only the hindmost, most frequently the 

 two hindmost, are of importance as serving as attachment for part of the appendix-muscles (those of 

 the glandular bag); as a consequence these rays have been somewhat bent, with the convexity turned 

 dorsally; the two hindmost are often partly, sometimes quite coalesced. 



With the primary skeletal parts, developed from the fin-stem, join, in the Plagiostomes, 

 several very differently shaped, calcified, secondary skeletal pieces, developed in the connective tissue, 

 surrounding the original, primary skeleton. These secondary pieces show, especially in the terminal part, 

 a considerable variation, both as to form and number, and the different genera, or even species, may 

 present rather important differences; but everywhere may be established the same fundamental type 

 that has been pointed out in the Greenland Shark. 



In the Plagiostomes the primary skeleton consists of: a large basale (B), and in continua- 

 tion of this one or more (until a number of four, Rkinobatus) shorter pieces (b u b 2 , etc.), and finally a 

 terminal joint, the appendix-stem (/»); this latter is always long, often considerably longer than 

 the other parts of the stem taken together. To these pieces must be reckoned one more, /?, placed 

 dorsally, parallel to the short stem-pieces b z , b 2 etc. ; most frequently it connects the basale with the 

 appendix-stem, but sometimes it does not reach the basale anteriorly, and is then connected with b x ; 

 in Rhina it is rudimentary, and only connects the last joint with the appendix-stem; in Narcine it 

 seems to be wanting. 



In quite young males of Plagiostomes (cp. fig. 2 in the text), even in embryos, all these primary 

 skeletal parts are already found; during the growth the terminal joint, the appendix-stem, is prolonged, 

 growing much more than the other parts, and calcifying to some degree in the surface (often to a 

 higher degree than any other part of the primary skeleton of the fin) always, however, with the 

 exception of the distal terminal part, this often wholly, and at all events at its base remaining 

 soft, and consequently flexible; this part of the appendix-stem I (after its form in the Greenland Shark 

 and many other Sharks) name the end-style {g). 



Contemporary with the growth and the calcification the secondary skeletal parts develop 

 around the appendix-stem, first as firm, fibrous parts, calcifying by degrees, and finally very hard; 

 some of them belonging to the terminal part are even shining, polished, and dentine-like; they then 

 rise, more or less naked, through the skin; this applies to one piece in Sonniiosiis , Lainna, Selachus, 

 Rkinobatus, Ra/a radiata; to two pieces in Acanthias, three (four) in Spinax etc. 



Two of the secondary skeletal parts are always closely connected with the appendix-stem, and 

 may even quite coalesce with it; these two cartilages form shorter or longer ridges, and are situated, 

 one dorsally, the other ventrally, connected with the appendix-stem in such a way as to form with it 

 the part of the appendix-slit that cannot be widened; they are the two marginal cartilages, the 



■) When A. Frits ch (Zool. Anzeiger, vol. 13. 1890, p. 31S, and Fauna der Gaskohle etc. Bohmens, vol.3. 1895) 

 restores the ventral appendages of the fossil Xenacanths as lateral structures, developed from rays, I am convinced that 

 he is wrong, and has misinterpreted the fossils. 



