376 MR. F. DAY ON RACES AND HYBRIDS [May 20, 



I, I fear, can speak most authoritatively of the accuracy of Semper's 

 statement : " An 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 Muller'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 fins. Polperro." 



4. On Races and Hybrids among the Salmonidse. — Part II. 

 By Francis Day, 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- 

 mouidse at Uowietoun, 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 milled 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 Salmonidse 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 Howietoun 2 , 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 my 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. Blomfield's account of 

 Myxine. 



2 An error appears in my former paper, at page 19, these fish having been 

 hatched in March 1881, not 1882. 



