24 



ON THE APPENDICES GENITALES iCLASPERS) IN THE SELACHIANS. 



hand its secreting part is especially developed, and its muscular wall somewhat more complicated. 

 In the part of the M. compressor forming the muscular wall of the bag, the direction of the fibres 

 may be rather different, but they chiefly radiate in bent lines towards the periphery, or round this 



to the dorsal surface; this latter is only by loose connective tissue 

 connected with the ray-muscles. In the part in the shaft the 

 direction is more straight, parallel to the axis; this is the case 

 with the fibres covering the lateral surface of the appendix-stem 

 (or a short proximal part of it), as also with those forming the 

 outer, lateral border of the appendix-slit. This lateral part most 

 frequently appears on the dorsal side as an independent muscle, 

 and might be called the outer lip-muscle , being, as it were, 

 separated from the other part of the wall of the bag by the at- 

 tachment of the fin-membrane. By a closer examination and by 

 a transverse section through this region (cp. fig. i and 14 in the 

 text) I have been convinced of its forming a whole with the other 

 parts of the muscular wall of the bag, with which also the corre- 

 sponding part in the Holocephales forms a complete union (see 

 later). A large part of this outer lip-musele» originates anterior- 

 ly from the piece /9 and the hindmost ray, or rays; posteriorly it 

 is inserted partly on the inner investment of the ventral marginal 

 cartilage, partly on the aponeurotic covering of the ventral termi- 

 nal pieces, and acts through this especially on the piece Tv. The 

 muscular coat formed by M. compressor will by contracting expel 

 the fluid secreted from the epithelium of the bag; but besides its 

 hindmost, lateral part, the outer lip-muscle , when it is long and 

 powerfully developed (as in Sharks with a short ventral marginal 

 cartilage, for inst Somniosus, Spinax , Acanthias, R/uiia), will 

 act antagonistically to M. dilatator, i.e. narrow the dilated terminal part, and lay the erected ter- 

 minal pieces. 



The muscular system of the appendix which here has been briefly represented in its typical 

 characteristics, shows in different Plagiostomes special modifications, as to which the reader is referred 

 to the special part I shall only here state that the part of M. compressor which appears as the outer 

 lip-muscle of the appendix-slit, commonly, as to its size and development, is adjusted to the length 

 of the ventral marginal cartilage; therefore it is very small in Scyllium (pi. VI, fig. 66, S), and in 

 1'ristiurtts, rather small in Raja (fig. 67, S); longer and more powerful in Torpedo, but especially de- 

 veloped in Sharks as Sommosus, Acanthias, Spinax, Rliina , a. o. From the part of M. compressor 

 wrapping the bag proper, is in the Rays developed a special muscular layer around the voluminous 

 gland found in these latter. In the Sharks (with the exception of Rkina) the inner epithelium of the 

 bag does not form real glands, but only contains secreting cells, and is accordingly very simple as 

 secreting apparatus. In the Rays, however, has been developed a bulky gland protruding as a 



Fig. 4. 



Acanthias vulgaris rj. The ventrals 

 seen from the lower surface. 5 M. com- 

 pressor, A M. adductor , D M. dila- 

 tator, R ray-muscles, T$ the < spur . 

 The stippled contour indicates the an- 

 terior extent in another specimen. 



