20 ON THE APPENDICES GENITALES (CLASPERS) IN THE SELACHIANS. 



itself being more or less rodshaped. This latter joint, I suppose, is the one that in the male is pro- 

 longed and developed into the appendix-stem, which never bears rays; otherwise, however, the number 

 of < intermediate joints» between the basale and the terminal joint (the appendix-stem in the male) 

 does not alwa)'s correspond in the two sexes of the same species, and the part of the stem situated 

 distally of the basale seems upon the whole to be rather varying in females of the same species"). In 

 the female, as was to be expected, all the secondary skeletal pieces are wanting, but besides those 

 also the piece /3 of the primary pieces. It is rather difficult to decide with any degree of certainty, 

 how this piece is to be interpreted; perhaps it might be done by following its development. The 

 smallest embryos (of Acaiithias) that I have had occasion to examine, however, have had this piece 

 quite independent, in the same position, and with the same relations as in the grown animal. This 

 piece, however, has to be considered as belonging, either to the stem, or to the rays, and in the latter 

 case it is, I think, to be regarded as one ray, there never being any mark of a composition of more 

 parts. In several species, as Trygon^ R/iiiiobafiis, it might, as to its form, remind of a ray, which then 

 was to be considered as displaced to a higlier level than the others, and turned parallel to the axial 

 stem; in Trygoii it must be the last, hindmost ray, while in Rliinobafus it could not be the last ra\", 

 as more real rays follow farther backward; and so on in the other species: if it was to be considered 

 as a ray, it must, in the different species, be a different ray, displaced and transformed. I think it 

 more probable that the piece /? belongs to the stem, and has been separated from this bj- a longitu- 

 dinal division, which might possibly be occasioned by the development of special muscles for the 

 appendix. 



In the Holocephales (see pi. I) all secondary cartilages are wanting in the fin-skeleton: it 

 is only composed of a large basale bearing all the rays, of a short piece /'i , the appendix-stem /', and 

 the dorsal piece [i. The walls of the appendix-slit are produced b\- a kind of rolling-up of the stem- 

 portions ^i, and h^ and thus the terminal part is only formed of the hindmost part of the appendix- 

 stem; this latter is rather differenth' formed in the two genera CluDKcra and Callorliynchus (see the 

 special part). 



The appendix-skeleton of the Holocephales accordingly is of a less compound construction 

 than that of the Plagiostomes, and that, as will be seen hereafter, is also the case with the muscular 

 system. Tliis simpler structure evidently in some degree repeats primitive features, btit these, on the 

 other hand, are connected with facts, that by no means are primitive, as for inst. the strongly marked 

 separation of the whole organ from the fin proper, the highly specialized form of the primary skeletal parts 

 — against the simpler form in the Plagiostomes (as the simple, rod-like shape of the terminal joint b etc.) — , 

 the connection with other, particular cojDulatory organs, etc.; these things, as well as many other facts 



') In two specimens of ventrals of female Greenland Sharks I find the structure different in the two sides of the 

 same pair of fins. In the left ventral of one specimen the basale is followed by a long and powerful joint, (bx + 62, fig- 3) 

 bearing two rays, and a ray-Uke httle terminal joint d\ in the right fin of the same specimen follow after the basale two 

 short joints (the distinction between those is indicated by stippling in fig. 3) /5i, ^2, each bearing one raj', and 62 also the 

 little ray-like terminal joint d\ thus on the left side a coalescing of i5i and 62 seems to have taken place. On the left side of 

 the other specimen follows after the basale only one sword-like, compressed piece, taking the place as the terminal joint, and 

 showing in its distal end, which is somewhat flattened, an indication of a longitudinal division; in the right side, on the 

 contrary, the basale is followed by a short joint {bi) bearing a ray and a compressed terminal joint (b). Consequently, if we 

 suppose a coalescing of bi and d on the right side, together with the last ray, we shall arrive at the structure on the left 

 side. As far as I have seen, the female fin-skeleton of Acanthias shows similar variations. 



