EFFECTS ON THE HIGHER INVERTEBRATES 39 



induced by lack of nourishment to assume the polyp-form, i.e., the larva form 

 of the species." Linko ('00) noted a disappearance of pigment in the ocelli of 

 the medusa Margellium retro punctatum which had been in an aquarium without 

 food for a long time. Citron ('02) found that in Syncoryne Sarsii the ectodermal 

 cells become flattened, the cytoplasm greatly reduced in amount, and the cells 

 fusing into a syncytial condition. 



In connection with his pioneer work on physiological morphology, J. Loeb 

 ('92) found that potassium must be present in small quantity in the surrounding 

 water to permit regeneration of polyps in Tubularia mesembryantheum, and 

 magnesium in addition to permit normal growth. Although at this time he 

 considered the salts of these two elements, in addition to NaCl, as sufficient for 

 regeneration and growth in Tubularia, he later (1905) admitted that traces of 

 calcium salts were also present in the water used. Herbst ('97) observed that 

 decapitated Tubularia mesembryantheum are able to regenerate their heads in 

 media free from calcium phosphate, perhaps because a sufficient supply was 

 already stored in the body. The further work of Loeb and Herbst will be 

 considered later in connection with the Echinodermata. 



Scyphozoa. — Among the Scyphozoa, deVarigny ('87) observed three 

 medusae of the jellyfish Aurelia aurita, weighing 98, 82 and 57 g., respec- 

 tively. After 150 days in the laboratory, two survivors weighed 82 and 75 

 g., representing a loss of %$ or ^ of the original weight. Since protozoa 

 and bacteria were not excluded from the sea-water, however, this probably 

 represents an incomplete inanition. 



Hadzi ('09) studied the effects of inanition upon larvae, probably of the Scy- 

 phomedusa Chrysaora mediterranea, in various advanced stages of development. 

 Upon placing the hydriform scyphulae in sea-water without food (excepting 

 the Ciliata present), the process of strobilization begins at once and many free- 

 swimming ephyrulae appear. On account of lack of food, the ephyrulae are 

 unable to develop further into Scyphomedusae, but undergo instead a series of 

 characteristic retrogressive changes. The umbrella becomes smaller, later 

 spherical, the marginal lobules and sense-organs (tentaculocysts) becoming 

 detached. The gut lumen becomes constricted; the gastric diverticula retract 

 and disappear. The body surface becomes ciliated. The reduced body later 

 assumes an ellipsoidal form (Gastrea type) with a simple mouth opening, which 

 finally becomes closed, resulting ultimately in a planula form, with distinct bound- 

 aries between ectoderm and endoderm. "Von einem iiber 1 mm. grossen, 

 schon ziemlich hoch differenzierten Tiere, der Medusenlarve Ephyra, ist unter 

 allmahlicher Riickbildung eine moglichst einfach gebaute, oft nur 80^ grossen, 

 Planula entstanden." This reversal of the developmental process is completed 

 within three weeks. The planulae may live fourteen days longer, but finally 

 lose their cilia and disintegrate. Certain modifications of the process may 

 occur, and the parent scyphula also undergoes similar regressive changes. 



Stockard ('10) noted that vigorous regeneration occurs in experiments upon 

 starving jellyfish, Cassiopea xamachana, but the corresponding decrease in body 

 size is greater than usual in starvation, since regeneration proceeds at the 

 expense of the older tissues. 



