LARVAE OF ARBACIA PUNCTULATA 



405 



yond the tri-radiate stage. Figures 132, 133 and 134 are from 

 culture g. They are still smaller than those of solution /, but , 

 in the main show the same characteristics. Figure 132 is com- 



Fig. 126 20d, 48 hrs. Skeleton somewhat more regular and less heavy than 

 the preceding, but an accessory skeleton on the left side has enlarged and devel- 

 oped most of the parts typical of a normal skeleton. 



Fig. 127 20e, 48 hrs. Skeleton heavier, reduced in size, irregular. No 

 accessory spicule. 



Fig. 128 20e, 48 hrs. Four centers present, all of about equal size and 

 highly abnormal. 



Fig. 129 20/, 48 hrs. Inhibition of growth very evident. Skeleton about 

 like that of a normal individual of 36 hrs. age. 



Fig. 130 20/, 48 hrs. Skeleton of about the same size as that of figure 129, 

 but more nearly of a true pluteus form. Irregular, and possessing accessory 

 rods. Accessory spicule present on the right side. 



Fig. 131 20/, 48 hrs. Four abnormal skeletal centers. 



Fig. 132 20^, 48 hrs. Inhibition of growth still more pronounced than in 

 figure 129. About like a normal individual of 18 hrs. 



Fig. 1.33 20g, 48 hrs. Specimen about the same size as in figure 132, but 

 with true pluteus form. Slightly irregular and with arm-rods unfused. Ac- 

 cessory spicule present. 



Fig. 134 20^, 48 hrs. Five spicules present, which are irregular and still in 

 the tri-radiate stage. 



THE JOURNAL OF MORPHOLOGY, VOL. 30, NO. 1 



