ON THE APPENDICES GENITALES iCEASPERS) IN THE SELACHIANS. 



r 9 



dorsal one (Rd), and the ventral one (Rv); posteriorly they always reach to the end-style, anteriorly 

 more or less forward, commonly not to the same length, and at most to the proximal end of the 

 appendix-stem. Together with this they form the chief piece* of the appendix-skeleton, a name 

 used by several earlier authors, who most frequently have not seen that this piece consists of 

 three parts. 



The other secondary cartilages, the terminal pieces, together with the end-style form the 

 skeleton of the terminal part, and are more or less movably connected mutually, with the marginal 

 cartilages, and with the end-style. The number of terminal pieces may be different, but in all Plagi- 

 ostomes two are found, one dorsal (Td), and one ventral (Tv), placed as a kind of movable continua- 

 tion of the two marginal cartilages, and with their inner edges joining the end-style of the axial 

 piece, which bv being bent (ventro-medially) is moved in connection with them; thereby they dorsally 

 withdraw more from each other, and the slit between them is widened. Only in a few cases (Trygon 

 violacea, Chlamydoselackus) these two pieces are found alone; in most Sharks a piece Td 2 is joined to 

 the lateral margin of Td, and imbedded together with 

 this in the dorsal lip of the appendix-slit; often a piece 

 Tv 2 is in a like manner joined to Tv\ further is gene- 

 rally found a piece T 3 , placed veutrally and laterally, 

 and often rising through the skin as a spur or thorn; 

 still more pieces may be developed (especially in Raja), 

 but their homologies in the different forms are gener- 

 ally easily pointed out, and are in the special part indi- 

 cated by the letters used. Finally may to the terminal 

 pieces proper be joined one or more « spurious- pieces 

 or covering pieces, enclosing like a shield the 

 terminal pieces, properly so called, on the dorsal side 

 (d) or the ventral side ('•); they are developed in the 

 aponeurosis of the 31. dilatator bespoken later on, which 

 otherwise wraps the terminal part, and serve as insertion 

 for part of this muscle. Such covering pieces are found 

 in all Rays and in some Sharks (for iust. Rhina). As 

 to the abundantly varied structure of the terminal part 

 the reader is referred to the special part; here I shall 

 only add that the simpler forms are generally found in 

 the Sharks, to which may be joined among the Rays 

 Torpedo, Narcinc, Rhinobatus and Trygon, while the 

 most complicated structures are found in the species 

 of Raja. 



Perhaps it may not be devoid of interest to compare the ventral skeleton of the male with that 

 of the female. In this latter we find the stem composed of a large basale and a different number 

 of shorter joints, among which the terminal one has no ray (typically), but often looks like a ray 



Kg- 3- 



Fig. 2. 



Fig. 2. Somniosus microcephalics, young o" (2 m 50cm). 

 The hindmost part of skeleton of left ventral (con- 

 siderably diminished). The letters as before. * an 

 intercalated extra-ray. 



Fig. 3. Somn. microcephalus, 5. The corresponding 

 part of skeleton of left ventral, ij + b 2 two coalesced 

 stem-joints; the stippled line indicates the distinction, 

 found between these joints in the right ventral of the 

 same specimen, b the terminal joint. Reduction as 

 in fig. 2. 



