54 PSEUDO-ENTOPHYTA, ETC. II. 



this stage destroy many which we, of course, never after see, because we never 

 seek for them. If the fungus has invaded the insect only to such an extent as 

 not to destroy organs immediately essential to its life, it may pass through its me- 

 tamorphosis into the imago, but with the posterior part of the abdomen filled with 

 a mass of fungous substance, as described above. 



The reason of the fungous production being always found in the last-mentioned 

 situation, arises, probably, from the fact that the access of the sporules to the inte- 

 rior of the animal is much easier through the generative and anal apertures than 

 through the more delicate passage of the proboscis. 



It is probable that this fungous disease of the seventeen-year locust is one of the 

 means of maintaining the equilibrium in the aggregate of the life of the species 

 under existing circumstances.^ 



' I say under existing circumstances, for if these change, the species may be either increased or dimi- 

 nished, or even extinguished ; but has not life in the aggregate ever been fixed in its extent ? If so, then 

 if a species be increased, diminished, or extinguished, the equilibrium of life in the aggregate has still 

 been preserved by another or several other species having diminished, increased, or primitively originated. 



