Chap. I. Homological Structures. 



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 t'.ie 

 higher animals, especially the anthropomorphous apes, is ex- 

 tremely close. 



Embryonic Development. — Man is developed from an ovulej 

 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 

 branchiaB which are not present in the higher vertebrata, though 

 the slits on the sides of the neck still remain (/, g, fig. 1), 

 marking their former position. At a somewhat later period, 

 when the extremities are developed, " the feet of lizards arid 

 " mammals," as the illustrious Yon 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, 14 " 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 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; 15 



After the foregoing statements made by such high autho- 

 rities, 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 



14 'Man's Place in Nature,' 1863, magnified^ the embryo being twenty- 



p 67. five days old. The internal viscera 



16 The human embryo (upper have been omitted, and the uterine ap- 



fig.) is from Ecker, ' Icones Phys.,' pendages in both drawings removed, 



1851-1859, tab. xxx. fig. 2. This I was directed to these figures by 



*mbryo was ten lines in length, so Prof. Huxley, from whose work, 



tnat the drawing is much magnified. ' Man's Place in Nature,' the idea of 



The embryo of the dog is from giving them was taken. H'ackel has 



Hischoff, ' Entwicklungsgeschichte also given analogous drawings in bis 



des Hunde-Eies,' 1845, tab. xi. fig. * Schopfungsgeschichte,' 

 42 B This drawing is rive times 



2 



