ON THE APPENDICES GENITALES (CLASPERS) IX THE SELACHIANS. 25 



thick, oval body from the dorsal wall of the bag into its inner space, and almost filling it; when the 

 ventral wall of the bag is opened, this body is immediately seen, and in sound animals it is sometimes 

 seen rather distinctly through the skin 1 )- Down the middle of the gland rnns straight or obliquely 

 (Trygon) a longitudinal furrow, in which is seen a great number of rather large holes with raised 

 margins: they are the excretory openings of collective dncts from a solid mass of large, dichotomously 

 divided, tubular glands. This gland is on all sides until the longitudinal furrow enclosed by a mus- 

 cular layer, originating from the dorsal muscular wall of the bag. By this special muscular layer the 

 secretion may evidently be ejected into the inner space of the bag, and then by contracting of the 

 muscular wall of the bag itself be driven on, partly through the large opening at the base of the 

 shaft, partly posteriorly through the tube , formed by the marginal cartilages, and 011 through the 

 terminal part; in full-grown animals these latter ducts are generally found filled with the secretion. 

 Among the Sharks I have only in Rhina found a similar bulky gland, but situated only in the shaft 

 (for further particulars see under Rhina). 



A survey of the medial fin-muscles in the females of the Plagiostomes will show that they 

 are of a considerably simpler structure than those of the male. In the female is found only one single 

 muscle, a M. adductor pinna (pi. V, fig. 63, 64, A) originating in quite the same way as in the male 

 from the pelvis and its aponeurotic prolongation in the ventral median line, and built in a similar 

 manner as to the division of the ventral side in separate bundles, the passing of the foremost lateral 

 part into the ray- muscles, a. s. o. ; here , too , the medial marginal portion forms a solid mass, continu- 

 ing as a posteriorly tapering bundle on to the terminal joint of the fin-stem 2 ). 



It is then -- especially considering the intermingling of fibres that often takes place in the 

 different muscles of the male -- an obvious conclusion that an adductor of a similar simple construc- 

 tion as the one, now found in the female, has been the origin of the J/, adductor, the J/, extensor, 

 and the M. dilatator, perhaps also of the J/, compressor of the male. When the hindmost joint of the 

 fin-stem developed into the appendix-stem, the distal part of the orginal, simple M. adductor might 

 be thought to be brought along at the same time, so that part of the deeper-lying fibres would origin- 

 ate from the stem-skeleton, by which process the J/, dilatator would arise; while in the proximal 

 part too a group of fibres originating from the stem separated as the M. extensor (in Lainua this 

 muscle is only part of the M. adductor). The .1/. compressor might have the same origin as the J/ 

 dilatator, but more likely it represents the very hindmost ray-muscles. 



In the males of the Holocephales ipl. VI, fig. 69 — 71) the separation between a proximal 

 muscular group and a distal one, placed on the appendix-shaft, is, as before mentioned, more strongly 

 marked than in the Plagiostomes. The proximal group is formed by a M. adductor, corresponding 

 to that of the latter, as to the detailed structure of which I refer to the special part; a separate M. 

 extensor is not found. The distal part is also here composed of a M. dilatator and a M. compressor, 



1 This gland was already seen long ago. J. Th. K 1 e i n ( Historise piscium naturalis promovendae missus tertius etc. cum 

 observationibus circa genitales Raja? maris etc. 1742), as far as I have seen, is the first author, who mentions it. He thinks 

 the gland to be a kind of testis (forte officina seminis |, but observes that he has not been able to find any connections 

 with the kidneys, nor with vesiculis seminalibus — adesse tamen possunt >. E. Olafsen in his Icelandic voyage (II p. 9S8) 

 takes the same view of the gland as Klein. 



2 ) The figure of Acanihias J given bv v. Da vidoff, 1. c. pi. XXIX, fig. 12, is not correct with regard to the direction 

 of the fibres; so I have given a new figure. 



The Ingolf-Expedition. II. 2, 4 



