Annual Address of V. T. Chambers, Esq. 81 



stated this is at the 3d and 5th moults in the respective groups, and 

 not at the 5th and 7th as I then believed, I have stated, in a preceding- 

 part of this address, that I have been unable to discover any trace of la- 

 bial palpi until this change in the form of the trophi takes place. But it 

 does not necessarily follow that they do not exist as mere rudiments or 

 points of growth. Neither have I observed any trace of the sexual organs 

 until that change takes place; nor of the wings until the last stage of 

 larval life. Yet other observers of larvie of other insects have detected 

 the genital organs at a much earlier stage, and also the rudiments of the 

 wings. Indeed, so many of the organs of the future butterfly or moth 

 have been detected in a rudiraentar}' condition, in its earliest stages, 

 that it may well be doubted whether any such thing as de^'elopmeat, as 

 distinguished from mere growth, takes place after the caterpillar 

 leaves the egg; that is whether there is any differentiation of new pai'ts 

 or organs after the caterpillar is excluded from the egg. After that, the 

 carterpillar and its organs gro'.v; and at state 1 times some parts grow 

 much more rapidly than others, and some are arrested in their growth. 

 or are even absorbed, so that they can no longer be seen ; but it seems 

 highl}^ probable that all the parts and organs of everj' future stage are 

 present at least as rudiments or points of growth in the caterpillar 

 when it leaves the egg. When one observes only the great and ap- 

 parentl}' sudden change from larva to pupa, and from pupa to imago, it 

 seems as if there has been all at once a great and almost entire change 

 of form and structure. But when one watches the gradual transforma- 

 tions of one of these semi-transparent larvse under the microscope, and 

 sees that all of this apparently sudden change is accomplished hy a 

 gradual though rapid growth of some parts, and the arrest or absorption 

 of others, he is led to the belief that there has been no differentiation of 

 anj' new organ, but that the whole change is accomplished simply by 

 growth and absorption of already existing organs. 



Swammerdam long ago stated that he "could point out in the larva 

 all the limbs of the future nymph or cnlex concealed beneath the 

 skin;" and this statement is probably substantiallj' true, though its 

 literal truth depends upon the period at which the observation is 

 made. The}- can be " pointed out " in the last stage of larval life, but 

 it would be difficult to point out some of them at earlier stages, how- 

 ever much from analogy we may be inclined to believe that they 

 nevertheless exist. Dr. Packard, in his " Guide to the Study of 

 Insects," states that " the body of the larva is transformed into that 

 of the imago; ring answering to ring, and limb to limb in both; the 

 head of the one is homologous with that of the other, and the 



