HOMOLOGICAL STRUCTURES. 8 



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 constitution, between man and the higher animals, es- 

 pecially the anthropomorphous 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 mem- 

 bers 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 (f, g, fig. 1), marking their former 

 position. At a somewhat later period, when the extremities are de- 

 veloped, "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 asser- 

 "tion may appear to be, it is demonstrably true." 



As some of my readers may never have seen a drawing of an 

 embryo, I have given one of man and another of a dog, at about 

 the same early stage of development, carefully copied from two 

 works of undoubted accuracy.'^ 



After the foregoing statements made by such high authorities, 

 it would be superfluous on my part to give a number of borrowed 

 details, showing 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 vari- 

 ous 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, "extending 



" 'Man's Place, in Nature," 1863, p. 67. 



1^ The human embryo (upper fig.) is from Bcker, 'Icones Phys.,' 1S51- 

 1859, tab. XXX. flg. 2. This embryo was ten lines in length, so that the 

 drawing is much magnifled. The embryo of the dog is from Bischoff, 

 'Entwicklungsgeschichte des Hunde-Bies,' 1845, tab. xL flg. 42 b. This 

 drawing is five times magnified, the embryo being twenty-five days old. 

 The internal viscera have been omitted, and the uterine appendages 

 in both drawings removed. I was directed to these figures by Prof. 

 Huxley, from whose work, 'Man's Place in Nature,' the idea of giving 

 them was taken. Hackel has also given analogous drawings in his 

 'Schopfungsgeschichte.' 



