324 THE WOELD OF LIFE 



this early period certain rudiments of wings and other organs 

 are represented by small groups of minute cells termed by 

 Weismann imaginal discs, which were determined by him to 

 be the rudiments of the perfect insect. These persist un- 

 changed through the whole of the active larval stage ; but as 

 soon as the final rest occurs preliminary to the last moult, a 

 most wonderful process commences. The whole of the internal 

 organs of the larva — muscles, intestines, nerves, respiratory 

 tubes, etc. — ■ are gradually dissolved into a creamy pulp ; and 

 it has further been discovered that this is effected through the 

 agency of white blood-corpuscles or phagocytes, which enter 

 into the tissues, absorb them, and transform them into the 

 creamy pulp referred to. This mass of nutritive pulp thence- 

 forth serves to nourish the rapidly growing mature insect, with 

 all its wonderful complication of organs adapted to an entirely 

 new mode of life. 



There is, I believe, nothing like this complete decomposi- 

 tion of one kind of animal structure and the regrowth out of 

 this broken-down material — which has thus undergone decom- 

 position of the cells, but not apparently of the protoplasmic 

 molecules — to be found elsewhere in the whole course of 

 organic evolution; and it introduced new and tremendous dif- 

 ficulties into any mechanical or chemical theory of growth and 

 of hereditary transmission. We are forced to suppose that the 

 initial stages of every part of the perfect insects in all their 

 wonderful complexity and diversity of structure are formed 

 in the egg, and that during the subsequent raj^idly growing 

 development of the larva they remain dormant ; then, that the 

 whole structure of the fully grown larva is resolved into its 

 constituent molecules of living protoplasm, still without the 

 slightest disturbance of the rudimentary germs of the perfect 

 insect, which at a special moment begin a rapid course of de- 

 velopmental growth. This growth has been followed, step by 

 step through all its complicated details, by ^Ir. Lowne and 

 many other enthusiastic workers , but I will call attention here 



