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Show 376 MR. F. DAY ON RACES AND HYBRIDS [May 20, I, I fear, can speak most authoritatively of the accuracy of Semper's statement: " A n Spirituspraparaten ist so gut wie Nichts von ihrem feineren Bau zu erkennen " 1. Finally, as to the systematic value of the Cuvierian organs we must, I think, agree with Semper that they are " viel weniger characteris-ticsh in ihren Formen fiir die einzelnen Gattungen, als es nach Miiller's Arbeiten scheinen konnte." At any rate, in no other organ does H. nigra display any character or combination of characters which would lead us to separate it off from the rest of the true Holo-thurise. The five specimens in the British Museum were obtained off the coast of Cornwall; two are said to have been " taken about some crab-pots, at a depth of 20 fms. Polperro." 4. On Races and Hybrids among the Salmonidae.-Part II. By FRANCIS D A Y , F.Z.S. [Received May 19, 1884.] On January 15th of this year (see P. Z. S. 1884, p. 17) I gave an account of the continuation of some experiments made by Sir J. Gibson-Maitland, F.Z.S., on the breeding and hybridization of Sal-monidse at Howietoun, and the inception of a few new ones. I propose in this paper to briefly remark upon their continuation, and how matters stood on March 13th, 1884. First, as to the hybrids between Salmon and Lochleven Trout. The oldest batch of these hybrids are the descendants from 20,000 eggs of the Trout milted from Salmo salar December 24, 1881, and which up to March 13, 1884, had been kept in a planked pond, 20 feet long by 5 feet wide. On this date those which remained (numbering 212), all of which appeared to be in perfect health, were removed to the octagon pond at Craigend. Among them, six were over 10 inches in length, but the majority were smaller, and some not above 2\ inches, showing the great range of variation in size of young Salmonidae raised from eggs and milt obtained at one time from the same parents although the resulting offspring are kept under exactly similar conditions of existence. I remarked in the paper referred to, that on Nov. 29, 1883, 4500 eggs of the Lochleven Trout (of the season of 1875) were milted from the parr of a Salmon raised at Howietoun2, and the eggs were placed in hatching-box No. 88. The number of eggs removed as dead during the following months were as follows :-in December 1 I have carefully compared M. Jourdan's account of the Cuvierian organs with the interesting account given by m y friend Mr. J. E. Blomfield (Q. J. M . S. xxii. p. 355) of the thread-cells of Myxine, but I cannot detect any points of similarity. Perhaps M. Jourdan will, in the further investigations which he has promised to make, direct especial attention to Mr. Blomlield's account of Myxine. 2 A n error appears in m y former paper, at page 19, these fish having been hatched in March 1881% not 1882. |