chap, xviil] MEDIAN DIVISION : GOLD-FISHES. 453 



ventral margin of the tail-fin. This groove may be extended up 

 through all the rays of the lower lobe of the tail, which then 

 consists of two tails side by side. The small dorsal lobe, which 

 lies above the notochord, is never involved in the jwocess, but always 

 remains single. There is therefore in this case no doubling of 

 the axis of the body. Examination of the skeleton shews that 

 in those fishes which have two tails the haemal spines of the last 

 three vertebrae are longitudinally split 1 and diverge to carry the 

 two tail-fins (Fig. 141, V). 



Pouchet lays stress on the fact that the size of each of the 

 paired tails is greater than that of the normal tail of a Gold-fish ; 

 but as Watase states that in the variety "Riukin" the tail may 

 be as long as the body, it is clear that this hypertrophy may exist 

 without any repetition. 



In cases where the anal fin is doubled the process is exactly 

 the same, resulting from a longitudinal splitting of the rays of 

 which it is composed. This may only affect the outermost parts 

 of the fin or may be carried up further so as to divide the inter- 

 hsemal spines, in which case the two anal fins arise from the 

 body wall at separate points and diverge from each other. 



Pouchet, who has extensively studied the history of Gold-fishes 

 in Europe, believes that it is almost certain that those which were 

 brought to Europe in the eighteenth century were all more or 

 less of the double-tailed order. He refers especially to the figure 

 given by Linnaeus 2 representing the double-tailed form as a normal. 



Pouchet states that the evidence goes to shew that this 

 anomalous race is not maintained in China by any rigid selec- 

 tion. He quotes a Chinese encyclopaedia to the effect that the 

 double-tailed Gold-fish is found in running streams, and gives 

 the evidence of Kleyn 3 , a missionary in China during the 

 eighteenth century, who states that "In fluvio Sleyn Gyprini 

 sunt qui caudam habent trifurcam et a piscatoribus Leid-brassen 

 vocantur, quasi diceres aliorum Cyprinoram conductor es." 



Though the duplicity of the hasmal spines may be unaccompanied by other 

 variations it should be noticed that the extraordinary "Telescope ' , Gold-fish not 

 unfrequently has also the double tail-fin. In the Telescope Gold-fish the eyes 

 project from the orbit to a greater or less extent, in the extreme form being 

 entirely outside the head and attached by a small peduncle only. The various 

 forms of abnormal Gold-fishes are generally to be seen in large quantities in 

 the shops of the dealers in aquariums &c. which abound near the Pont Neuf in 

 Paris. One of these dealers told me that he bred considerable numbers of them 

 every year, and that in fish from the same parents there was little uniformity, 

 many normals being produced for one that shewed any of the extreme variations. 

 It is recorded that of the Gold-fish hatched in Sir Robert Heron's menagerie about 

 two in five were deficient in the dorsal fin and two in a hundred or rather more had 

 a "triple" [sc. three-lobed as described above] tail-fin, and as many have the anal 



1 It should be observed that there is no want of original union between the 

 hasmal spine3, for these close in the haemal canal as usual. The phenomenon is 

 thus altogether different from that of spina bifida in the neural spines. 



2 Fauna suecica, 17-15, p. 331, PI. II. 



3 Kleyn, Miss., v. p. 62, Tab. xm. fig. 1 [not seen], quoted by Baster, Opusc. 

 subsec, Harl., 1762, p. 91, note. 



