SPECIALITIES OF THESE RELATIONS. 407 



of like structure with itself. In this case, as in the last, abun- 

 dant food is combined with low expenditure. These larva) are 

 found in such habitats as the refuse of beet-root-sugar fac- 

 tories — masses of nitrogenous cUbris remaining after the 

 extraction of the saccharine matter. Each larva has a 

 practically-unlimited supply of sustenance imbedding it on 

 all sides. 



It is true that some other maggots, as those of the Flesh-fly, 

 are similarly, or still better, circumstanced ; and, it may be 

 said, ought therefore to have the same habit. But this does 

 not necessarily follow. Survival of the fittest will determine 

 whether such specially-favourable conditions result in the 

 aggrandisement of the individual or in the multiplication of 

 the race. And in the case of the Flesh-fly, there is a reason 

 why greater individuation rather than more rapid genesis 

 will occur. For a decomposing animal body lasts so short a 

 time, that were Flesh-fly larvae to multiply agamically, the 

 second generation would die from the disappearance of their 

 food. Hence, individuals in which the excessive nutrition 

 led to internal metagenesis, would leave no posterity ; and 

 natural selection would establish the variety in which greater 

 growth resulted. All which the argument requires is, that 

 when such reversion to agamogenesis does take place, it shall 

 be where the food is unusually abundant and the expenditure 

 unusually small ; and this the cases instanced go to show. 



§ 360. The physiological lesson taught us by Bees and 

 Ants, not quite harmonizing with the moral lesson they are 

 supposed to teach, is that highly-fed idleness is favourable to 

 fertility, and that excessive industry has barrenness for its 

 concomitant. 



The egg of a Bee develops into a small barren female or 

 into a large fertile female, according to the supply of food 

 given to the larva hatched from it. We here see that the 

 germ-producing action is an overflow of the surplus remain- 

 ing after completion of the individual ; and that the lower 



