THE EVIDENCE FROM THE LIFE-HISTORIES OF INSECTS. 271 



in the scale, retrograding from Campodea, we may even conceive of 

 the stock from which that insect itself has sprung. Campodea 

 within the egg must pass through the stages common to all animals 

 at a like stage of development. There is a stage in the Arthropod 

 type when the young of the insect or crustacean is little else than a 

 footless, imperfectly developed worm. There is even a worm-like 

 larva of an insect allied to the gnats, which corresponds to such a 

 description ; and such low insect-larvae become irf turn obviously 

 related in form to certain low creatures allied to the worm kith 

 and kin. One of these low forms (Lindid) is depicted in Fig. 182. 

 This legless organism is related to the well-known " Bear-animalcules," 

 and Rotifers, or Wheel-animalcules. Its jaws resemble those of the 

 larval flies ; it has a ringed body, and in other respects exhibits a 

 close likeness to the young of many insects. Possibly, therefore, 

 in some such primitive root, common to a whole host of animals, 

 we may find the dim, ill-defined starting-point whence, led towards 

 Peripatus, and by Campodea, the insect tribes have grown into the 

 brilliance and aerial grace which mark their ranks to-day. 



It may not be unprofitable, at the close of our investigation 

 into insect history, to remind ourselves of the great problem which 

 their development has lent its aid in part to solve. At the risk of 

 apparently unnecessary repetition, let us keep in view that every 

 such history, however its individual terms are to be accounted 

 for, forms a link of greater or less importance in demonstrating 

 the great law of evolution, modification, and adaptation as the 

 true method whereby Nature has wrought out the endless variety of 

 the children of life. Especially useful and important, moreover, 

 is the history of the insect as illustrating the changes which the 

 adaptation and modification of the young form may effect in the his- 

 tory of a species. So far from the chrysalis or pupa being a stage in 

 the ancestry of the insects, we have seen that it represents merely a 

 secondary and acquired phase of their development. As Fritz 

 Miiller has succinctly formulated it, "the historical record pre- 

 served in developmental history is gradually EFFACED as the 

 development strikes into a constantly straighter course from the 

 egg to the perfect animal, and it is frequently SOPHISTICATED by the 

 struggle for existence which the free-living larvae have to undergo." 

 These words sum up the reason why insects in their metamorphoses 

 exhibit all gradations and shades, from mere moulting of skin to 

 complete change of form through a chrysalis state. Primarily they 

 undergo a metamorphosis because they happen to leave the egg at a 

 relatively early period of development ; but they share " metamor- 

 phosis " using the word in the broad sense with every other living 

 being. It is this plainly discerned series of changes which has 

 chiefly given to the study of entomology its fascination in the past. 



