FACTS FOR THE THEORY OF EVOLUTION. 



105 



ing example of the unity of type of the jointed appendages of 

 insects, and articulates generally. 



Another point of interest in these degraded insects is, that 

 the process of degradation begins either late in the life of the 

 embryo or during the changes from the larval to the adult, or 

 winged state. An instance of the latter may be observed in the 

 wingless female of the canker worm, so difl'erent from the winged 

 male ; this difl'erence is created after the lai'val stage, for the 



caterpillars of 



both sexes are 



the same, so far 



as we know. So 



with numerous 



other examples 



among the 



moths. In the 



louse, the em- 

 bryo, late in its 



life, resembles 



the embryos of 



other insects, 



even Corixa, a 



member of a not 

 remotely allied family. But just before hatch- 

 ing the insect assumes its degraded louse physiognomy. The 

 developmentist would say that this process of degradation 

 joints to causes acting upon the insect just before or immedi- 

 ately after birth, inducing the retrogression and retardation of 

 development, and would consider it as an argument for the 

 evolution of specific forms by causes acting on the animal while 

 battling with its fellows in the struggle for existence, and per- 

 haps consider that the metamorphoses of the animal within the 

 egg are due to a reflex action of the modes of life of the ances- 

 tors of the animal on the embryos of its descendants. 



125. The Turkey Louse. 



12G. Antennae of 

 Goniodes. 



