ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. '295 



dominant over the pyramidal, their figures showing an intermediate type. The 

 early development of the arms is not dominant over the late development, but an 

 intermediate type is again shown, with perhaps a slight inclination towards the 

 late condition. A rough skeleton is not dominant over a smooth, but once more an 

 intermediate condition is shown. The strong development of the "Mittelstab" is 

 dominant, but all that can be said about the " Aufsteigender Ast" is that it is 

 usually present. 



Now with regard to these characters in the late 14-day larvae (figs. 40-43 of their 

 paper), it is impossible to form any opinion, as no 14- day pure-bred S. franciscanns 

 are given for comparison. The following conditions would seem to hold regarding 

 them : — The clubbed character of the skeleton is dominant, but it is impossible to say 

 anything about the round form of the larva. The early development of the arms is 

 intermediate with regard to the late condition, but on this head it is impossible to be 

 definite. The skeleton is intermediate in character between rough and smooth. 



The strong development of the " Mittelstab" is dominant, and the " Aufsteigender 

 Ast " is present. 



In the cross 5. franciscanus $ X S. purpuratus $ , with regard to the four-day 

 larvae shown in their figures 46, 47, it is impossible to make any assertions, as they 

 are stunted and o})viously unhealthy. In the case of the six- to seven-day larvae 

 shown in their figures 48-55, the clubbed condition of the skeleton is dominant, as is 

 likewise the round form of the larva. The late development of the arms is doubtful. 

 The character of the skeleton is again intermediate between the rough and the 

 smooth condition. Most of these larvte show a rudimentary " Mittelstab " and an 

 "Aufsteigender Ast." 



Instead of having six dominant characters always present in both reciprocals, the 

 above-described figures would seem to show the following to be the case : — 



1. The clubbed skeleton is present in both reciprocals. 



2. The skeleton is usually intermediate with regard to roughness. 



3. The "Aufsteigender Ast" is usually present. 



The other characters are dovd^tful. 



Not enough figures are given to prove or disprove their points. With regard to 

 ill-health, they say that in the cross S. franciscanus $ X >§. jmrpuratus $ , "man 

 erhiilt nur eine kleine Menge normaler Plutei," and that only a small number reach 

 the pluteus stage. The figures of this cross that they give (figs. 46-55) show 

 obviously stunted and imhealthy larvae. 



They state that figs. 54 and 55 show dominance of the clubbed form and inhibition 

 of development (p. 362, line 1). This would seem, however, to apply to all the 

 figures of this cross, with exception of perhaps figs. 48 and 51. This being so, the 

 only point clearly pi-oved is that both reciprocals develop the clubbed skeleton. The 

 other points seem doubtful, owing to the unhealthy development of the cross 



