EFFECTS ON THE HIGHER INVERTEBRATES 



49 



was likewise found necessary for development of the fertilized ova» Even with 

 CaS0 4 and CaCl 2 present in the solution, the development proceeds no further 

 than an abnormal pluteus, with rudimentary skeleton (Fig. 22). The presence 

 of CaC0 3 was found necessary, not only for the development of larvae with a 

 normal skeleton, but also for the preservation of the already formed skeleton in 



em 



Fig. 17. Fig. 16. Fig. 18. 



Figs. 16 to 25 illustrate the effects of various salt deficiencies upon the development 

 of the sea-urchin, causing inhibition or distortion of the normal growth process. After 

 fertilization in normal sea-water, the ova were placed in artificial media containing various salt 

 mixtures. The normal controls in the complete salt mixtures pass through the segmentation 

 stages, blastula (Fig. 25) and gastrula stages, reaching the normal pluteus stage shown in 

 Fig. 16. All these figures (16 to 25) are taken from the monograph by Herbst ('97). 



Figs. 17 to 24 represent the most advanced stages reached in the solutions variously 

 deficient. (After Herbst '97.) 



A, arms; a, a, a — segments of alimentary canal; Be, blastocele; Cc, (abnormal) ciliated 

 crown; em, egg membrane; m, mesoderm cells; Sk, skeletal rods; Sp, "snout-like" process; 

 Vac, vacuoles in blastula cells. 



Fig. 16. — Normal pluteus stage of the sea-urchin Echinus, reared in a complete salt mixture 

 containing NaCl, KC1, MgS0 4 , CaSCu, CaCOs, FeCOs, and CaHP0 4 . Fourth day. 



Fig. 17. — This stage of (abnormal) segmentation represents the maximum development 

 reached in the same salt mixture as the foregoing (Fig. 16), with omission of the phosphate. 

 Most of the ova failed to segment at all, or were arrested in still earlier stages of abnormal 

 segmentation. This illustrates the necessity for phosphorus in normal development of the 

 sea-urchin, Echinus. 



Fig. 18. — Abnormal gastrula of Echinus, representing the maximum stage of development 

 reached in an S-free mixture of NaCl, K'Cl, MgCl 2 , Ca 3 P 2 8 , CaCOs and FeC0 3 . Third day. 

 Shows that sulphur is necessary, for normal development. 



experiments beginning with the pluteus stage. Finally, the fertilized ova and 

 later stages were observed to undergo retarded and abnormal development 

 unless iron was present, at least in traces (Fig. 23). 



The abnormal form and structure of the larvae appeared variable, yet to 

 some extent characteristic according to the type of deficiency, as shown by 

 Figs. 16 to 25. Herbst reached the general conclusion that "Das wichtigste 



