32 INANITION AND MALNUTRITION 



by the adult nutrition. Cuenot ('99) doubts whether the sex-ratio is notably 

 affected by nutrition in species reproducing by fertilization only. 



Underfeeding during the larval period may also result in undersized adults 

 (various insects), and also sometimes in marked structural modifications (pig- 

 mentation, etc.). In some cases, these acquired characters appear hereditary, 

 at least for a few generations; although ultimately upon adequate diet there is 

 an evident tendency to return to the original condition. 



The experiments with media or diets variously deficient have shown that 

 compounds of P, K, Na, Ca, Mg, Fe, S and CI appear necessary for development, 

 growth being inhibited or variously perverted when the amount stored in the 

 ovum is exhausted, unless a supply from without is available. The remarkable 

 results (especially of Herbst, Loeb and Maas) in this field have been summarized 

 by Driesch ('06). The marvelous effect of fat upon the development of the 

 reproductive tract in the female Hymenoptera illustrates the morphogenetic 

 potency of a single dietary factor. As to other forms of partial inanition, 

 Baumberger holds that protein is in general the limiting factor in the growth of 

 insects. The fruitfly Drosophila apparently requires yeast as well as sugar for 

 growth, and other insects living on fermenting substrata of low protein content 

 usually feed on the microorganisms present. Little or nothing is known con- 

 cerning the possible requirement of vitamins by the invertebrates in general. 



Regeneration during Inanition. — In many of the invertebrates, indications 

 of regenerative activity may be observed in certain cells or regions during the 

 general degenerative process of involution. Driesch ('01) observed that the 

 reserve materials of the body which are consumed during starvation may be 

 used to build up other parts of the organism. Thus in daphnids, Crustacea and 

 insects, repeated ecdysis (moulting), with regeneration of a new exoskeleton 

 and appendages, may occur during starvation. This regenerative process occurs 

 notably in the lower invertebrates, such as the sponges and coelenterates, and 

 has been studied especially in planarians. Here the starving organism exhibits 

 the remarkable capacity to regenerate large portions of the body, such as the 

 head, with all its parts, pharynx, nerve ganglia, musculature and excretory 

 system. Thus even during starvation, regeneration may restore a complete 

 normal individual of much smaller size. In this process there is an extensive 

 involution of the older tissues to furnish material for the regenerated parts. 



Recovery upon Refeeding. — In general, it is possible for the starving inver- 

 tebrates to recover their normal size and structure upon appropriate refeeding, 

 if the process of involution has not proceeded too far in degeneration. This 

 applies also to partial inanition. In sponges, for example, the skeleton is 

 reformed upon restoring calcium carbonate to the medium. In planarians, 

 regeneration of the gonads is possible even when they have nearly disappeared 

 after three or four months of inanition. In the gland cells of the snail Helix 

 starved five months, evidences of recuperation were found even after only two 

 days of refeeding. Drosophila (fruitfly) larvae are capable of normal develop- 

 ment after long periods of retardation on inadequate diet; and in this form/as 

 likewise in the larvae of the beetles Trogoderma and Tribolium, the normal per- 

 iod of life may be greatly extended by retarding the developmental process 



