406 



GRACE MEDES 



parable to 129, but indicates a slightly less advanced condition. 

 .Figure 133, like 130, is more irregular and possesses an acces- 

 sory spicule. In 134, five spicules are present, but are small 

 and even at this stage show decided irregularity of form. 



Fig. 135 20a, 72 hrs. Control. 



Fig. 136 20e, 72 hrs. Skeleton smaller than control, but fairly normal. 

 Large accessory skeleton on the right, fused to the primary at the base of the 

 arm-rods. 



Fig. 137 20/, 72 hrs. Asymmetrical. Several rods in each arm, with spines 

 missing from the right. Accessory skeleton on the right side, with all the typi- 

 cal parts. The anal rod of the secondary skeleton forms an accessory arm; and 

 the oral rod of the secondary functions instead of the oral rod of the primary, 

 which is missing on this side. 



Fig. 138 20/, 72 hrs. Slight irregularities. Spines missing from the right 

 side. Left oral arm is exceedingly heavy, while that on the right is of very 

 light structure and possesses an accessory rod. 



Figure 135 represents a larva from the control 72 hours old. 

 In figure 136, solution e, the primary skeleton is smaller than 

 the normal, but otherwise is fairly regular. In the right side 

 there is a large secondary skeletal structure, consisting of arm- 

 rods fused to about the same extent as those in the primary, short 



