2 2 READINGS IN BIOLOGICAL SCIENCE 



the species, is strikingly the same in all mammals, from the first act of 

 courtship by the male, co the birth and nurturing of the young. Monkeys 

 are born in almost as helpless a condition as our own infants; and in certain 

 genera the young differ fully as much in appearance from the adults, as do 

 our children from their full-grown parents. It has been urged by some 

 writers, as an important distinction, that with man the young arrive at 

 maturity at a much later age than with any other animal: but if we look 

 to the races of mankind which inhabit tropical countries the difference 

 is not great, for the orang is believed not to be adult till the age of from 

 ten to fifteen years. Man differs from woman in size, bodily strength, 

 hairiness, &c., as well as in mind, in the same manner as do the two sexes 

 of many mammals. So that the correspondence in general structure, in 

 the minute structure of the tissues, in chemical composition and in con- 

 stitution, between man and the higher animals, especially the anthropomor- 

 phous apes, is extremely close. 



EMBRYONIC DEVELOPMENT 



Man is developed from an ovule, about the 125th of an inch in diameter, 

 which differs in no respect from the ovules of other animals. The embryo 

 itself at a very early period can hardly be distinguished from that of other 

 members of the vertebrate kingdom. At this period the arteries run in 

 arch-like branches, as if to carry the blood to branchiae which are not 

 present in the higher vertebrata, though the slits on the sides of the neck 

 still remain, marking their former position. At a somewhat later period, 

 when the extremities are developed, "the feet of lizards and mammals," 

 as the illustrious Von Baer remarks, "the wings and feet of birds, no less 

 than the hands and feet of man, all arise from the same fundamental 

 form." It is, says Prof. Huxley, "quite in the later stages of development 

 that the young human being presents marked differences from the young 

 ape, while the latter departs as much from the dog in its developments, 

 as the man does. Startling as this last assertion may appear to be, it is de- 

 monstrably true." 



After the foregoing statements made by such high authorities, it would 

 be superfluous on my part to give a number of borrowed details, shewing 

 that the embryo of man closely resembles that of other mammals. It may, 

 however, be added, that the human embryo likewise resembles certain 

 low forms when adult in various points of structure. For instance, the 

 heart at first exists as a simple pulsating vessel; the excreta are voided 

 through a cloacal passage; and the os coccyx projects like a true tail, "ex- 

 tending considerably beyond the rudimentary legs." In the embryos of 

 all air-breathing vertebrates, certain glands, called the corpora Wolffiana, 

 correspond with and act like the kidneys of mature fishes. Even at a 

 later embryonic period, some striking resemblances between man and the 

 lower animals may be observed. Bischoff says that the convolutions of the 



