EFFECTS ON THE HIGHER INVERTEBRATES 4 1 



into normal scyphostomata, the larvae disintegrating in P-free solutions. Simi- 

 larly in potassium-free mixtures, the planulae developed no further, but gradu- 

 ally died off within seven days; while controls developed normally. 



Ctenophora. — In connection with his experiments on partial inanition with 

 various salt deficiencies, Herbst ('97) incidentally noted that when segmenting 

 ova of Beroe ovata are placed in mixtures free from calcium phosphate, they soon 

 perish; while the controls continue development. 



PLATYHELMINTHES 



Of the Platyhelminthes or flatworms, the class Turbellaria or planarians 

 have been studied most extensively during inanition. Some observations 

 have also been made upon the Nemerteans, a related group of somewhat doubt- 

 ful classification. 



Turbellaria. — F. F. Schultze ('36) was apparently the pioneer in observing 

 the marked reduction in the size of planarians during protracted inanition. The 

 first recorded measurements, however, are those of Voigt ('94), who noted that 

 in ten or eleven months of fasting the length of Planaria alpina is reduced from 

 12 mm. to 1 3^ or 2 mm. The sexual reproduction is also affected, the "cocoons" 

 being reduced to less than half their normal length, and the number of young 

 from each being reduced from 55 in the well-fed to four in the starving individ- 

 uals. Cuenot mentions that asexual division in some Turbellaria {Microstoma, 

 Planaria subtentaculatd) " tres prospere dans les moments d'abondance, s'arrete 

 lorsque la nourriture devient rare." According to Rywosch and Zacharias 

 {'86),' however, the advent of unfavorable conditions may lead to the develop- 

 ment of sex-organs, with return to sexual reproduction. 



Lillie ('00) observed that in 43 days of starvation a Planaria maculata was 

 reduced from 9 mm. (length) and 0.75 mm. (breadth) to 0.6 mm. and 0.25 mm. 

 Assuming a decrease of one-half in the third (dorsoventral) dimension, this 

 involves a reduction to V90 of the initial volume. The sex-organs appear 

 immature. The pigment cells near the surface seem greatly reduced in number, 

 but not in size. Although no detailed histological examination was made, the 

 reduction process apparently reverses the steps of normal development. " Cer- 

 tain it is that specimens reduced by starvation to a smaller size than just hatched 

 specimens of the same species resemble these in their general proportions, the 

 relatively greater breadth in proportion to their length, as compared with mature 

 specimens, the smallness of the cephalic lobes, and in the small number of intesti- 

 nal diverticula and branches of the longitudinal nerves." During regeneration, 

 Lillie also noted considerable loss, owing to the destructive metabolism in work- 

 ing over the old tissues into new form. 



Morgan ('01) observed that if regenerating Planaria lugubris are fed, the 

 old tissue loses but little and the new tissue grows faster; if the worms are unfed, 

 the old tissue loses more and the new part grows less, forming a smaller worm. 

 The decrease in the old part appears to be due, not to cell-migration, but to 

 loss of substance, which is transported to the regions of active regeneration. 



Stevens ('01) found a remarkable resistance of the nervous tissues to inani- 

 tion in Planaria lugubris. "The nerve fibres are more easily traced in speci- 



