On Mendelian Dominance. 



173 



apart to a greater degree in some cases than in others. A large 

 number of drawings with the camera lucida were made each day. 

 For the sake of clearness I have given in the figures illustrating 

 this paper, drawings of but two representative plutei of each culture 

 each day. These are drawings made with camera lucida. They 

 therefore show the relative size of franciscanus and purpuratus larvae. 

 A comparison of the juvenile plutei (Figs. 1, 2, and 3) shows the 

 hybrid to differ very little from the pure purpuratus except for the 



Fig. 7. 



Fig. 8. 



Fig. 9. 



cross-bars in the former. The pure franciscanus larvae are more 

 advanced in the development of arms but otherwise the shape differs 

 scarcely at all from Figs. 1 and 2. By the beginning of the fourth 

 day the franciscanus plutei (Fig. 6) have attained complete develop- 

 ment both as to spininess, length of arms, and body shape. The 

 hybrid (Fig. 5) only occasionally has spines at this stage , the arms 

 are somewhat longer than the pure purpuratus (Fig. 4) but the body 

 shape is much the same. Twenty-four hours later the franciscanus 

 plutei (Fig. 9) have the same form as on the day before , but the 

 hybrid (Fig. 8) shows slightly longer arms, a body shape more like 



