1911.] 



Studies in Heredity. 



:197 



performed with the species Echinocardium cordatum and Echinus esculentus. 

 The results which were obtained are almost at total variance with those 

 which Vernon records. A word or two, therefore, on the conditions 

 under which the experiments were carried out may be in place. 



In the end of June, 1911, I went to Millport, on the Clyde, and through 

 the courtesy of the Director, Mr. Eichard Elmhirst, I was accorded the use 

 of a table in the Biological Station of the West of Scotland Marine Biological 

 Association. I desire to record my gratitude to the Director and also to 

 Dr. Gemmill, Vice-President of the Association, for the help they gave me 

 in my experiments. My thanks are also due to the staff of the Zoological 

 Department of the University of Glasgow, from whom I obtained the loan of 

 apparatus. I remained at Millport during the months of July and August, 

 and had abundance of the urchins of both species at my disposal. In fact, at 

 low spring tides, Echinus and Ecliinocarclium could both be obtained by the 

 bucketful within a comparatively short distance of the laboratory. Both 

 species were sexually ripe, and in both cases I was able to rear the normally 

 fertilised eggs through a great portion of their developmental cycle. 



In the case of Echinus esculentus the larvse lived for four weeks and 

 developed their epaulettes, and all the eight larval arms. Doubtless it 

 would have been an easy matter to rear them through their metamorphosis 

 into the adult form, but as I had previously worked out the development of 

 this species in great detail I gave no special heed to the larvae. 



In the case of Echinocardium cordatum, however, I was able to rear large 

 numbers of the larvse through the whole of their larval development, and saw 

 them metamorphose into young urchins under my eyes. I used a culture of 

 the diatom Mtschia as food in the case of both species, and for this I am 

 indebted to Dr. Gemmill. 



Now the artificial fertilisation of the eggs of Echinocardium which Vernon 

 carried out resulted in the production of only a comparatively small pro- 

 portion of larvae, and these lived at longest only about eight days. It may 

 be added that, according to my experience, all Vernon's larvse were sickly, 

 and their development went forward very slowly. In my cultures, larvae 

 three days old were more advanced in development than his larvse when they 

 were five days old. I think, therefore, that it will be conceded that my 

 material was in a much healthier state than that which was at Vernon's 

 disposal. 



In fig. 1, a pure-bred larva of Echinocardium cordatum six days old is 

 represented. It will be observed that the rudiments of eight larval arms 

 are already to be seen. The " post-oral," or " anal " arms (as they are often 

 designated by German writers), which are the first to develop, are fairly 



2 G 2 



