408 



GRACE MEDES 



spines are missing from the arm-rods, while in the left they are 

 abundant and are heavy and irregular. In this side the oral 

 arm is abnormally massive, whereas the corresponding struc- 

 ture in the opposite side is slender and has an accessor}^ rod. 

 In fieure 137 a secondary skeleton is present in the right side. 



144 



1 146 



Figs. 143 to 146 Experiment 20. Stale sea-water. 



Fig. 143 20aa, 24 hrs. Three spicules present, radially arranged, but irregular 

 in form. 



Fig. 144 '20aa, 24 hrs. Three centers again present, but extremely irregular. 

 One spicule is -small and abnormal, but has some of the typical parts, — body-rod, 

 arm-rods and lateral connective. ^One is still tri-radiate, while the third is in 

 the form of a straight rod. 



Fig. 145 20ao, 48 hrs. Skeleton on right side somewhat irregular, but pos- 

 sessing all the normal parts excepting dorso-ventral connective and oral arm- 

 rod. On the left side these are present but the body-rod is incomplete. That 

 of the right side has bent forward and is developing a compensator}^ structure. 



Fig. 146 20aa, 48 hrs. Onlj^ one skeletal structure present which lacks dorso- 

 ventral connective and aniil arm. 



It possesses arm-rods, dorso-ventral connective and body-rod 

 with ventral branches by which it is fused to the primary skele- 

 ton. It is also joined by what apparently corresponds to the 

 lateral connective. Its anal rod is not so closely applied to 

 that of the primary skeleton, as are those in the specimens pre- 

 viously considered, pjid here the pluteus has developed an ac- 



