300 THE WORLD OF LIFE CHAP. 



of the successive moults, but it being more advantageous to 

 have the larva stage wholly in the form best adapted for the 

 storing up of living protoplasm, the retrogressive variations 

 became step by step earlier, and at length occurred within 

 the egg. At 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 unchanged 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 thenceforth 

 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 

 decomposition of the cells, but not apparently of the proto- 

 plasmic molecules to be found elsewhere in the whole 

 course of organic evolution ; and it introduced new and 

 tremendous difficulties 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 rapidly 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 develop- 

 mental growth. This growth has been followed, step by step 

 through all its complicated details, by Mr. Lowne and many 



