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On fs Echinus Hybrids. 



H. M. Fuchs. 



An investigation on inheritance in hybrids between the three EngHsh 

 species of Echinus was carried out in the Marine Biological Laboratory, 

 Plymouth, during 1909-1912 by C. Shearer, W. de Morgan, and H. M. 

 Fuchs. In a paper published in the Phil. Trans. Royal Soc, Ser. B, 

 Vol. CCIV., p. 255, the results of this work were described in detail. At 

 the time of publication, E. miliaris had been raised from the egg to 

 maturity in the laboratory, in the course of one year, and a second 

 generation had been obtained from these individuals, but none of the 

 hybrid urchins had as yet reached maturity. This year, however, some 

 of the hybrids have become sexually mature, and from them a second 

 hybrid generation has been raised. 



The urchins which have formed ripe genital products are four in- 

 dividuals of the cross E. esculentus $ X £'. acutus 3' (referred to below as 

 EA), derived from fertilizations made in 1912. The largest of these 

 urchins now measures 6 cm. in diameter, exclusive of the spines. On 

 May 11th, 1914, two of these hybrids laid eggs in the tank in which they 

 were kept. Naturally these eggs could not be used for experimental 

 purposes, since they were deposited in the sea water of the aquarium 

 circulation, and therefore not under sterile conditions. On June 6th 

 I induced three of the four to deposit genital products without cutting them 

 open, under conditions which excluded the possible presence of foreign 

 eggs or spermatozoa. It is hardly necessary to mention here that, as in 

 all the previous work on Echinus hybrids, the fact of the complete absence 

 of such sperm was made certain by controls of unfertilized eggs, none of 

 which segmented. Two of the three hybrids from which genital products 

 were obtained proved to be females and one a male. The sperm from the 

 latter gave 100% fertiHzations with the eggs of the former, yielding 

 healthy larvae. 



From this it is seen that hybrids between the species E. esculentus and 

 E. acutus are perfectly fertile and that a healthy Fg generation can be 

 obtained from them. When a larger number of these F^ hybrids have been 



