346 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



DoNCASTER and Gkay, and they have established that a true fusion of $ and ? 

 pronuclei invariably took place in all cases. In the segmentation stages there may, 

 or may not, be an elimination of a definite number of chromosomes. We have 

 raised hybrid urchins to a late stage from all the material examined by these 

 authors. 



11. We have not succeeded in correlating tlie character of inheritance with any 

 fixed condition of chromosome elimination, but, on the other hand, we have not shown 

 that such correlation does not take place. 



12. The inheritance of a character of the young urchins immediately after meta- 

 morphosis has been investigated, but it was found to be too variable to give certain 

 results. 



13. With regard to the characters of our adult hybrid urchins : — 



(«) The cros.s E. esculentus % X E. acutus $ has grown the quickest, and has 

 attained the greatest size, measuring some 8' cm. across the spines at the end of 

 the first year. In this cross it is'difiicult to say which parent the hybrids resemble 

 most, on account of the absence of fixed specific difierences in the parent forms. 

 The least variable character is the absence of oral spines in E. acutus. None of 

 the hybrids of this cross have oral spines ; in this respect, therefore, they resemble 

 the paternal parent. In general pigmentation and shape of spines again, they 

 approach more the paternal than the maternal parent. We occasionally, however, 

 find E. acutus with oral spines, and the pigmentation varies within wide limits. 

 In the shape of the test, they resemble more E. esculentus than E. acutus. On 

 the whole, it is perhaps safe to say that the hybrid urchins of this cross are, more or 

 less, intermediate between both parent forms. 



[h) Next to the above-mentioned hybrids the urchins of the cross E. miliaris ? X 

 E. acutus $ have grown the most rapidly. We have a large number of urchins of 

 this cross living. In this cross we have distinctive characters in each parent form. 

 In general it may be said that maternal characters predominate ; for example, the 

 presence of a primary spine on all the ambulacral plates, the distinct plates of the 

 buccal membrane, and the general green colour. The number of secondary spines 

 would also seem to denote maternal influence, although this may be a matter of size. 

 It should be noted, however, that the maternal characteristics are not so pronounced 

 in the hybrids as in the maternal parent, recalling the inheritance of the larval 

 features. The pedicellarise, however, are paternal, as for instance the trideutate and 

 the triphyllous, but the globiferous are clearly intermediate between both parent 

 species, as shown by the toothing. 



(c) The remaining crosses have failed to attain any size, or have produced such 

 abnormal urchins, that they can hardly be considered. 



14. It is probable that hybridization takes place in nature between E. esculentus 

 and E. acutus in those localities in the vicinity of Plymouth where their habitats 

 coincide. A considerable number of intermediates— among them individual which 



