26 DARWINISM AND EVOLUTION. 



The first heart of the human embryo has a structure such as 

 appears permanently only in animals like worms : — a simple 

 pulsating chamber. 



As the embryo assumes its vertebrate character, it developes 

 certain gill-clefts [See Plate, fig. man, A.~\ on each side of the neck, 

 up to which arteries run in curving branches. [See Plate, fig. Z>.] 

 This arrangement which remains constant in the fish, and which 

 indeed is suitable only for a water-breathing apparatus, soon 

 undergoes modification [See Plate, fig. man i?.] and becomes 

 entirely altered [See Plate, fig. J2.~\ before the foetus is required to 

 breathe air. The useless vessels are generally absorbed, but in 

 some instances remain as rudiments. 



At a later period, there is a movable tail considerably longer 

 than the legs, as is permanently the case in many mammals. 



As foetal evolution progresses, we find the arms longer than 

 the legs, the soles of the feet turned towards each other, and the 

 great toe projecting sidewise from the foot, as in adult apes ; 

 while during the sixth month the whole body is covered very 

 thickly with hair, extending even over the face and ears, every- 

 where indeed save on the lower sides of the hands and feet, which 

 are also bare in the adult forms of monkeys. Thus we may tell 

 our valued friend, who goes about like a Manx cat, protesting 

 that at any rate he is not descended from a monkey, — we may tell 

 him that he himself was once covered with hair from head to foot ; 

 and that . his own blameless person was once adorned with a 

 movable tail, whatever may have been the case with his ancestors. 



As the different stages of foetal development represent not only 

 the changes through which the entire race, through countless ages, 

 has passed, but represent also what are permanent forms in some 

 animals, it might be asked, if the foetus were removed from the 

 parent at one of these early stages, would its development be 

 arrested, and would it remain permanent in its fish-form, or in its 

 quadrupedo-caudal form, as the case might be ? 



The common eft of our ponds passes a good deal of its time in 

 the water, and lays there a large number of eggs. The young one 

 on emerging from the egg is furnished with water-breathing gills, 

 which after some weeks are dropped, and the animal becomes an 

 air-breather. As the Alps were slowly raised, and pools of water 

 grew gradually scarcer, the efts in that part of the world, influ- 

 enced by the law of Natural Selection, underwent certain changes 

 which kept them in equilibrium with their environment, and 

 became entirely terrestrial. Oviposition, being at last no longer 

 possible in water, was more and more delayed so that now the 

 Alpine salamander, as it is called, though it has at the commence- 

 ment of the breeding season 40 to 60 eggs, yet matures only two, 

 for which the remaining eggs serve as food material. Notice 

 particularly that from the moment of its birth, the young is an 



