362 ON THE EXPEEIMENTAL HYBRIDIZATION OF ECHINOIDS. 



Fig. 124. — Aboral view of two well-marked varieties of E. miliaris found at 

 Plymouth. On the left, short-spined variety from Wembury Bay. On 

 the right, loiig-spined variety. 



Fig. 125. — Aboral view (natural size) of an E. miliaris raised in the laboratory, 

 one year old. This urchin was raised from the egg of the short-spined 

 variety of E. miliaris shown in the left-hand figure of fig. 124. It 

 will be noticed that it approaches more the long-spined type, although 

 both its parents were the short variety. This individual urchin, bred 

 in the laboratory, discharged on two occasions a large quantity of eggs, 

 from which we are at present rearing a second generation. 



Fig. 126. — Aboral view of a young hybrid urchin of the cross E. esculentus % X 

 E. acutus S , natural size, one year old. The comparison of this figure 

 with fig. 123 will give some idea of the rapid rate of growth of this cross 

 within the period of twelve months, fig. 123 representing the same hybrid 

 from the aboral and oral surfaces, but about twelve months later. 



Fig. 127.— Aboral view of hybrid urchin of the cross E. miliaris % X E. acutus $ , 

 one year old, slightly less than natural size. 



