EFFECTS ON THE HIGHER INVERTEBRATES 53 



materials (including disintegrating pigment cells ) from the regions undergoing 

 atrophy to those where further growth occurs. Thus, by a process of "auto- 

 differentiation," further development (e.g., anlages of the pedicellariae) may 

 occur at the expense of the remainder of the body. The inanition involution is 

 therefore not purely a reversal of the normal developmental process. Runn- 

 strom refers the morphological changes directly to physico-chemical conditions, 

 varying with the food supply and resulting differences in the acidity, permeabil- 

 ity, etc. of the various cells and tissues. 



Asteroidea. — The experiments of Herbst ('97) upon the effects of various 

 salt deficiencies, which have already been described for the sea-urchin larvae, 

 were also in some cases extended to the developing starfish (Asterias glacialis) 

 with very similar results. In phosphorus-free salt mixtures the fertilized ova 

 fail to segment normally and development never goes beyond the blastula stage. 

 Bipinnaria stages in phosphorus-free solutions die within a day. Sulphur 

 (sulphates) and potassium salts were likewise shown to be necessary for the 

 normal early development of starfish. Tests were not made for the other sub- 

 stances found necessary in the development of the sea-urchin. 



Mead ('oo) obtained great differences in size between fed and unfed starfish. 

 He noted that sexual maturity is correlated with the attainment of a certain 

 size (50 mm.). "When food is accessible, the starfish eats voraciously and 

 grows with great rapidity, but, on the other hand, it will live for months almost 

 without food and apparently remain healthy, though it does not grow." 



Schultz ('08b) kept recently metamorphosed larvae of the starfish Asterias 

 rubens in filtered water to see whether they undergo a "reduction" to embryonal 

 form as he found in Hydra and Planaria. Growth ceases, but no developmental 

 reversion occurs. At the end of three weeks, most of the starfish show no change 

 in size or structure, excepting the intestinal gland-cells or granule-cells, which 

 become fewer and may disappear entirely. Even in more prolonged starvation, 

 no typical "reduction" occurs, but degeneration gradually supervenes. The 

 cells of the epithelial band soon become detached. Proliferated and degen- 

 erated cells fill all the cavities of the body, the gut-lumen first, and the stone- 

 canal last. The lumina of the blood-vessels and water-vascular system become 

 obliterated, and the body cavity filled with connective tissue. The muscle 

 and nervous system persist unchanged, however, and the size of the nuclei in 

 general is unaffected. 



MOLLUSCA 



Of the phylum Mollusca, the effects of inanition have been studied chiefly 

 in the class Gastropoda, with a few observations upon the Pelecypoda. 



Gastropoda. — The remarkable resistance to inanition by the snail Helix 

 was noted by several earlier observers cited by Lucas (1826). Helix (sp.?) 

 was said by Macbride (1774) to endure starvation for a period of 15 years! For 

 Helix nemoralis, Miiller noted a period of one year. For Helix pomatia, 

 Sorg (1805) observed endurance for six months, and Wiesmann for one year. 

 Semper ('81) stated: "I myself kept various species of land-snails for years 



