ON THE APPENDICES GENITAU3S (CLASPERS) IN THE SELACHIANS. 73 



dorsal side (fig. 69) the muscle stretches considerably farther backward than 011 the ventral side, rea- 

 ching to the spot, where the appendix-slit passes to the medial side. 



The muscle of the glandular bag, M. compressor, arises from the lateral edge of the 

 piece ,? (see fig. 69), and is inserted on the lateral surface of the piece 6 Z , and on the appendix-stem, 

 as also on the folded ventral edge of this latter. The fibres seen on the ventral side (fig. 71), pass 

 from the edge of ,} round the calf , running obliquely or transversely, so that part of them is in- 

 serted perpendieularlv on the appendix-stem; those seen from the dorsal side, on the contrary, run 

 straight from before backward, and they form the lateral limit of the appendix-slit, and are attached 

 where the edge folded from the ventral side, is prolonged as the dorsal terminal branch (fig. 69). The 

 opposite, medial, lip of the appendix-slit is formed by the M. dilatator. 



Into the described, very voluminous muscle the dermal fold representing the glandular bag in 

 the Plagiostomes , sinks from the dorsal side through the appendix-slit. This structure has here evi- 

 dently remained in a state of development as that, with which it begins in the Plagiostomes; by a 

 transverse section we see that the bag may in reality be called rudimentary, as it only fills very 

 little in comparison with the powerful wrapping muscular mass. If we imagine this invagination to 

 grow verv much forward and ventrally, we may get a structure resembling that in the Plagiostomes; 

 part of the bag will then be situated on the ventral surface of the fin itself, and the muscular coat- 

 ing will, as it were, be extended to a thinner wrapping layer, while the part keeping its position 

 along the outer edge of the slit, will retain its original appearance and become the lip-muscle . This 

 dermal bag, which in Chimcera is so small, and whose inner surface is quite smooth and shows no 

 special gland, can nevertheless give plenty of secretion; this fact is proved by the abundance of fluid, 

 partly filling the bag, partly adhering to the branches of the terminal part, and also filling the 

 corners between the base of the fin and the body; on the last-mentioned place it may be supposed 

 to have flown from the foremost, larger, roundish opening of the appendix-slit. 



I have not a quite clear understanding of the influence of the muscles of the appendix-shaft on 

 the terminal part ; however, I think it likely that by a contemporaneous action of both the said muscles 

 a -- probably rather slight — distension of the three terminal branches may be brought about, the M. 

 dilatator acting on the medial branch, the M. compressor on the two others; by this action the con- 

 tinuation of the appendix-slit between the medial and the dorsal branch would be opened. That also 

 here the M. compressor will serve for the pressing out of the secretion of the glandular bag , seems 

 to me to admit of no doubt. 



As to the pelvic appendage (fig. 70, 71,/), to which nothing corresponding is found in 

 the Plagiostomes, it is in Cliimcrra rather simple; its contour is tolerably spoon-shaped, and it bears 

 on the surface that in the position of rest is turned ventrally (but which will accordingly be turned 

 dorsally, when the organ is directed forward), a soft, loose, unpigmented or slightly pigmented dermal 

 cushion, while the membranous skin of the opposite surface fits tightly to the skeleton. For moving 

 this organ has only one muscle (fig. 69, w), by which it can be raised in such a way as to come out 

 of its pouch 1 ), when it is able to take hold with the toothed edge. This muscle is very powerful^ 



") Comp. also G arm an: On the Pelvis and External Sexual Organs of Selachians etc. Proc. Boston Soc. Nat. Hist. 

 Vol. 19, 1S76 — 78, p. 199. 



The Ingolf-Expedition. II. 2. 



