150 



SCIENCE. 



[N. S. Vol. XXIII. No. 578. 



groups or ' nests ' near the basal membrane, 

 their increase in size (growth) and migration 

 toward the lumen, with an accompanying new 

 formation of surrounding cytoplasm. The 

 vigor of nucleus and cytoplasm seems to he 

 exhausted after the secretion and discharge of 

 a certain amount of digestive fluid, and rapid 

 and perfectly obvious senescence and histolysis 

 take place. Inspection of cross-sections of 

 the ventriculus of any feeding caterpillar will 

 show this normal physiological regeneration 

 phenomenon in most illuminating manner. 

 While this reg'enerative process was, when first 

 noted, considered to be a part of that extensive 

 general histolysis and histogenesis which regu- 

 larly accompanies the post-embryonic develop- 

 ment of insects with ' complete metamor- 

 phosis,' it is now known — thanks especially to 

 Needham's discriminating work — to be a phe- 

 nomenon also accompanying or incident to 

 diges4:ion, occurring all through the feeding 

 life of the insect, and not limited to that 

 period in late larval life (pre-pupal life) when 

 the radical histolysis of the larval organs 

 occurs, preparatory to, or coincident with, the 

 new-building (histogenesis) of the imaginal 

 (adult) organs. There is, however, probably 

 always a markesj and unusual degree of re- 

 generation of alimentary epithelium during 

 the prepupal and early pupal stages, i. e., at 

 the time of the radical transformation phe- 

 nomena. This has been recently well shown 

 in the case of the water-beetle Cyhister, by 

 Degeener.* 



A more striking phenomenon, or group of 

 phenomena, of physiological regeneration in 

 insects is that extraordinary double process 

 of degeneration and moulting on the one hand 

 and regeneration and complete new-building 

 on the other which characterizes the ontogeny 

 (in post-embryonic life) of the insects with 

 so-called ' complete metamorphosis,' i. e., those 

 insects which come from the egg in a form 

 (larva) radically different from that of the 

 definitive adult condition. From the butter- 

 fly's egg there hatches a caterpillar without 

 wings, without compound eyes, with eight 

 pairs of legs, with minute, short two- or three- 



> Zool. Jahrb., v. 20, pp. 499-676, 1904. 



segmented antennae, with biting and chewing 

 mouth-parts composed of heavy mandibles, 

 jaw-like maxillse, and flap-like labimn, with 

 musculature for worm-like and creeping loco- 

 motion, and with simple, straight alimentary 

 canal for the manipulation and digestion of 

 bits of solid food (leaves, etc.). But the but- 

 terfly into which the caterpillar develops has 

 wings, compound eyes, long, many-segmented 

 antennse, only three pairs of legs, sucking 

 mouth-parts composed of a curious long flex- 

 ible tube made up of the maxillae alone, with 

 mandibles wholly wanting and labium reduced 

 to a small fixed sclerite, complex musculature 

 for flight, and a long twisted alimentary canal 

 with conspicuous sac-like diverticula for hold- 

 ing and digesting flower nectar. In even 

 greater degree do the larva and adult of the 

 Diptera and Hymenoptera differ, and in only 

 slightly less degree those of the Neuroptera 

 and Coleoptera. Now in all these specialized 

 insects the development from larva to adult 

 (usually achieved in a few days or weeks) is 

 not accomplished by a slow, gradual transfor- 

 mation of the parts of the larva into those of 

 the adult, but is distinguished by the curious 

 fact that many, if not most, of the larval 

 organs are either wholly cast aside by moult- 

 ing at the time of pupation, or undergo a 

 radical histolysis resulting in complete dis- 

 integration. The larval mouth parts and an- 

 tennae are completely discarded at pupation 

 (last larval moulting) and have their places 

 taken by wholly new and usually markedly 

 different mouth parts and antennse; the larval 

 musculation, parts or the whole of the ali- 

 mentary canal, the salivary glands and Mal- 

 pighian tubules, and parts or the whole of the 

 tracheal system degenerate, and have their 

 places taken by radically new muscles, ali- 

 mentary canal, salivary glands, Malpighian 

 tubules and -trachefe, produced (regenerated) 

 from elementary cell groups called histoblasts 

 or imaginal buds. This phenomenon of whole- 

 sale histolysis and histogenesis characteristic 

 of all the members of all the orders of insects 

 with complete metamorphosis (with some 

 Coleoptera and some Neuroptera the break- 

 down and new-building is slight) is to be 

 looked on as a wholesale and extreme case of 



