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Preliminary Notice on the Experimental Hybridization 



of Echinoids. 



By 

 Cresswell Shearer, Walter De Morgan and H. M. Fuchs. 



JFith 7 Text Figures. 



INDEX. 



I. Introduction and previous work. 

 II. Material. 



III. Methods. 



IV. Description of external characters of normal and hybrid ]arv?e : 



a. E. esculentus $ x E. csculentas'i . 



b. E. miliaris S '.< E. esculentus 9 . 



c. E. miliaris $ x E.miliaris ? . 



d. E. esculentus i x E. miliaris ? . 



e. E. acutus 6 x E. acutus ? . 

 V. Characters of the skeleton. 



VI. The chemical control of inheritance. 

 VII. The characters of the young sea-urchin. 

 VIII. Summary of conclusions. 



I. Introduction and Previous Work. 



This paper is a preliminary account of a series of experiments on the 

 hybridization of Echinoids, first commenced by one of our number 

 <De Morgan) at Plymouth in 1909, and which will form part of 

 a larger work now approaching completion. This will comprise the 

 hybridization of Echinus amtus, E. esculentus, and E. miliaris, together 

 with an account of the cytology of the hybrid crosses and the control 

 of paternal and maternal influence by chemical means.* 



Within the last two decades a large amount of attention has been 

 devoted to the problem of parental influence in Echinoderm hybrids. 

 Most of this work has been done at Naples, where the majority of sea- 

 urchins seem to possess a longer breeding period than those of the 

 colder waters of our own coasts. In America within the last year or 

 two considerable attention has been devoted to this subject. In the 

 hands of different oljservers, liowever, this work has led to very con- 

 flicting results, and has proved most indecisive in settling the main 

 points at issue. 



In 1889 Boveri (3) was the first to investigate the hybrids between 



* The full paper will contain a large number of skeleton figures and drawings of Plutei 

 and coloured plates of the hybrid urchins. The investigation of the cytology has been 

 undertaken by L. Doncaster, and will form Part II of the paper. 



NEW SEIUES. — VOL. IX. NO. 2. Of'TOBEU, 1911. I 



