such perfection as we find in the human infant at birth. Precisely so 

 was it with the race. The lowly Moneron was of homogeneous struc- 

 ture, possessing neither parts nor kind, but gradually differentiating into- 

 nucleus and cell ; its descendants, the Gastrceada, becoming possessed,. 

 by a process of invagination, of an external layer of nucleated cells and 

 an internal and more delicate layer, thus forming a hollow organism, or 

 Gastrula. This external cellular integument was the original sense- 

 organ of the animal kingdom, from which developed the organs of spe- 

 cial sense. Though without nerve and special sense-organs, yet these 

 little hollow Gastroeada, and, in fact, their ancestors, the Amoebae, which 

 consisted of simple protoplasmic cells, each enclosing a nucleus, were 

 possessed with sensory perception, being influenced by light, and by 

 variations of pressure and temperature. As the evolutionary process 

 continued, and the animal kingdom assumed higher forms, the original 

 epidermal general sense-organ became converted into several special 

 organs of sense, each specialisation commencing with a simple depres- 

 sion upon the integument of the organism ; numerous little epidermal 

 nerves of perception were formed, which could perceive changes of 

 pressure and of temperature, and some of which gradually became en- 

 abled to understand particular influences affecting them, such as those 

 produced by a strong odour, light-waves, and sound-waves. By adapta- 

 tion, the extremities of these sense-nerves became expanded and en- 

 larged, so as to enable them the better to understand the particular 

 influences ; and this expansion was accompanied by a corresponding 

 depression on the integument, which cup-like formation afterwards 

 became converted into an eye, or other organ of special sense, very 

 imperfect in the invertebrate forms of life, imperfect in the fish, more 

 perfect in the amphibian, and still more perfect in the mammal forms, 

 such as apes and men. In short, the life-history of the individual is an 

 exact counterpart in miniature of the life-history of the species up to 

 the particular point reached by the particular individual. 



The order and mode of development is precisely the same in 

 all animal organisms, and may be conveniently studied by placing a 

 hen's egg in an incubating machine, and carefully watching it for the 

 space of three weeks. It will be observed that the eye, ear, nose, and 

 mouth are not present at the commencement of the process, but make 

 their appearance later on, about the third or fourth day of incubation, as 

 tiny depressions on the integument, from which condition they gradu- 

 ally develop into perfect organs of special sense, as possessed by the full- 

 grown chicken ; the eyes, which receive the impressions caused by light- 

 waves; the ears, which receive those made by sound-waves; the nose, 

 by which odours are discerned ; the mouth, which holds the taste-organ; 

 and the skin, which remains the organ of touch and perception of tem- 



