IX.] RETROGRESSTVE DEVELOPMENT IN NATURE. 2 J 



ants have no such instincts ; they care nothing for their own 

 young, and the species would become extinct, if they were 

 suddenly deprived of their slaves. So it is not only among men, 

 that there is a curse upon slavery ; even animals become 

 degraded by it. 



Other species of slave-making ants are known, and have 

 been carefully studied, in which the degeneration of the masters 

 goes even farther and affects their physical strength. But so 

 much remains unexplained in the life-history of these species, 

 that I will not treat of them here, remarkable as are the obser- 

 vations which have been made about them. All these examples 

 afford further support to our theory of retrogressive develop- 

 ment as a result of disuse ; for the above-mentioned cases of 

 the degeneration of instinct took place in worker-ants, i. e. in 

 animals which have not the power of propagating their species. 

 Hence the disappearance of the instincts in question cannot 

 be due to the hereditary transmission of any degeneration 

 acquired by individuals in consequence of the fact that they 

 were not required to seek their own living. 



In the cases above quoted, the instinct of feeding has not 

 entirely degenerated, but only a part of it has been lost, viz. the 

 instinct of seeking food and the power of recognizing it by sight. 

 Evidence is, however, forthcoming to show that the whole 

 instinct of feeding is sometimes lost, so that actually no hunger 

 is felt and no nourishment taken. This may sound very 

 strange, but it is an undoubted fact that there are animals 

 which absorb as much nourishment in the larval stage as 

 will last them during the rest of their life. Many moths, 

 especially among the Bomb3^ces, possess very degenerate 

 mouth-organs, and so do the Ephemeridae : all these take no 

 sort of food. In male Rotifers the alimentary canal is entirely 

 wanting ; they have neither mouth, stomach, nor intestine ; their 

 lives are of such short duration that the food material with which 

 they begin life is sufficient to sustain them throughout it. 

 There is no luxury in nature ; no instinct and no organ in the 

 body can persist unless absolutely essential to the life of the 

 species. Panmixia — in other words, the cessation of the opera- 

 tion of natural selection — removes all that is superfluous, only 

 leaving that which is absolutely necessary. 



But, of course, if our theory, be the right one, such retro- 



