90 INSECT PHYSIOLOGY 



The phagocytic haemocytes are sometimes actively concerned in 

 removing this disintegrating tissue and making it available to the 

 growing organs of the adult, but there is no clear evidence that the 

 haemocytes initiate this process. 



The co-ordination of all these processes to produce the adult form 

 is the problem of orderly growth which is at present quite unsolved. 

 The potentialities of form seem generally to be inherent in the tissues 

 themselves (wings, eyes, integument, &c.) and to be more or less 

 independent of the other organs in the body. Though the develop- 

 ment of the muscles at metamorphosis seems often to depend upon 

 their connexion with the central nervous system. 



Regeneration 



The general obscurity of the factors controlling growth is well illus- 

 trated by the phenomena of regeneration. In the adult insect the 

 capacity to heal wounds, with the formation of new cuticle, persists ; 

 but there are no extensive powers of regeneration. In the pupa the 

 same is true ; if the developing wings in the pupa of Tenebrio are cut 

 short, they round themselves off and approximate to the normal 

 form, but there is no true regeneration of tissue. If the wing germs of 

 Lepidoptera are mutilated in the last larval stage, the damaged areas 

 of pattern are not made good; whereas if this is done in the preceding 

 instar, wings of normal proportions but reduced size regenerate ; and 

 if the germ is divided, reduplicated wings result. At a still earlier 

 stage, the wing germs can be extirpated completely and are formed 

 anew from the hypodermis. Clearly throughout development, as 

 differentiation proceeds, there is a progressive loss of totipotence and 

 regenerative power; in the pupa everything is finally determined ex- 

 cept for relatively slight changes in colour pattern. In hemimetabo- 

 lous insects, if the appendages are removed in the early larval stages, 

 they show progressive regeneration at succeeding moults, and may 

 attain almost normal proportions by the time the insect becomes 

 adult. Here again there is a progressive loss in regenerative power as 

 the insect grows older, which is due partly, but not entirely, to the 

 reduction in the number of moults in the older insects, and the 

 corresponding reduction in the opportunities for growth. 



In all these cases, the removal or partial removal of an organ 



