Larval Dimorphism 



changed until the nymphosls. By virtue of a 

 remarkable variation, revealing a new vein of 

 observation to the entomologist, the Anthrax- 

 flies, in the larval state, assume two successive 

 shapes, differing greatly one from the other, 

 both in structure and In the part which they 

 are called upon to play. I will describe this 

 double stage of the organism by the phrase 

 larval dimorphism.' The Initial form, that 

 issuing from the egg, I will call 'the primary 

 larva;' the second form shall be 'the secon- 

 dary larva.' Among the Anthrax-flies, the 

 function of the primary larva Is to reach the 

 provisions, on which the mother is unable to 

 lay her egg. It Is capable of moving and en- 

 dowed with ambulatory bristles, which allow 

 the slim creature to glide through the smallest 

 interstices in the wall of a Bee's nest, to slip 

 through the woof of the cocoon and to make 

 Its way to the larva intended for Its succes- 

 sor's food. When this object is attained. Its 

 part Is played. Then appears the secondary 

 larva, deprived of any means of progression. 

 Relegated to the Inside of the Invaded cell, as 

 incapable of leaving it by Its own efforts as it 

 was of entering, this one has no mission in life 

 but that of eating. It is a stomach that loads 

 itself, digests and goes on adding to Its re- 



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