270 Appendices to Fifth Annual Report 



found in a cartilaginous condition when their thicker portion is already 

 more or less ossified. Arising from the vertebrae near the base of the last 

 described wedge-shaped hypural is a narrower bone of uniform thickness, 

 which passes backwards and slightly downwards, so that arising dorsal to 

 the median lateral line of the body, and therefore at the base of what 

 principally composes the upper lobe of the caudal fin, it terminates closely 

 applied to the upper distal corner of the ventral wedge-shaped hypural 

 which chiefly supports the lower lobe ; thus this median bone serves to 

 bind the lower lobe of the fin firmly to the upper.* Finally, lying along 

 the upper edge of the dorsal wedge-shaped bone, is another stout, rod- 

 shaped shorter hypural or haemapophysis of what appears in the fish to 

 be the 60th vertebrae, and beyond it again another similar but still shorter 

 bone (PI. XVIII. fig. 28). In the herring fry of 27 mm. length each of these 

 bones is provided with a somewhat nodular-like head, connected with the 

 main portion by a rather narrower neck, which, although not forming 

 aperture, is applied to the still well-marked vertebra, and bears a con- 

 siderable resemblance to the bases of the last undoubted haamapophyses, 

 and especially would do so if these were coalesced.! 



In nearly all respects the herring's tail bears a much nearer resemblance 

 to that of the trout than of any other fishes which I have examined. 



The Unpaired Fins. 



The rays of the caudal fin proper are 19 in number (an occasional — or less 

 than 2 per cent. — -variation from this occurs). In addition to these are 

 three, sometimes four, short accessory rays (unsplit, but jointed like the 

 others) already referred to, which form the dorsal and ventral edges of the root 

 of the caudal fin, and are borne principally by the neural bones of the 57th 

 vertebra, and the thickened haemal spine of the 55th vertebra respectively. 



The 19 caudal fin rays are all ventral to the notochordal axis, and are 

 not arranged symmetrically — there being ten rays in the upper lobe and 

 nine in the lower ; that is to say, the tenth ray counting from either the 

 dorsal or ventral edge of the fin is not the central ray so far as the centre 

 line of the body, or the apparent homocercal form of the fin, is concerned. 

 Excluding the short accessory rays, the outermost (the 1st and 19th) rays 

 of the fin are the longest and thickest. They are unsplit longitudinally 

 and laterally, but are jointed transversely to their tips, in lengths in a large 

 herring of from 6 to 1 mm., there being from about 55 of such joints in the 

 outer, to 25 or 30 in the central rays. The proximal joints are directly 

 transverse, and form an irregular articulation, but they gradually become 

 more diagonal towards the end of the ray. In the young fish these 

 segments are always relatively and often actually longer than in the old 

 fish. In a 40 mm. long herring the basal segments measured about 1J 



* It is rather remarkable that in several fishes the appearance here is similar — a 

 dorsal and ventral expanded hypural with a narrower rod-like bone diagonally 

 situated between them. I am inclined to think from its appearance and situation 

 (not directly on a vertebra, fig. 28) that it is not a true hypural, but possibly an 

 ossified ligament. 



t Since the above observations w r ere made, I have seen Ryder's excellent paper 

 giving details of an extensive examination of the median and paired fins of fishes 

 (Evolution of the Fins of Fishes, U.S. Com. of Fish and Fisheries Report for 1884 

 [published 1886]). My observations on the herring and sprat, although not specially 

 made for this purpose, as well as an examination of the caudal fin in trout, catfish 

 (Anarrhichas), and some other unidentified larval fishes, almost entirely corroborate 

 Ryder's statements. I incline to believe, however, there is a further spread of 

 cartilage between the hypurals of the herring than represents these bones entirely, 

 but I have been unable to procure the young fish from 15 to 25 mm. length, and have 

 therefore missed their complete development. 



