250 HOMOLOGICAL RELATIONS OF THE 



would be more suitable, as now commonly restricted to 

 correspondences in function. There is a wide difference, 

 however, between the reproductive function and others, in 

 the constancy of its structural relations. Whether it is 

 that the process, whereby are laid the foundations of the 

 organized fabric, has, as it were, reflected back upon it some 

 of the uniformity of system, which is so striking a character- 

 istic of the latter, or whatever other explanation may be 

 suggested, so it is, as a general rule, that not only have 

 the reproductive organs as definite relations in each great 

 group as any part of the fundamental framework of the 

 skeleton, but that even in animals of totally different types 

 of organization, there prevails a close uniformity of struc- 

 ture, even in very minute details of these parts, the evolu- 

 tion, both of ova and spermatozoa, presenting with some 

 few exceptions the closest resemblance throughout the 

 whole Animal Kingdom. 



It is true that the interpolated process of gemmation 

 observes no such constancy, so that the uniformity is very 

 much confined to the gamomorphic or sexual stage ; but as 

 the phenomena of this stage form the starting point of the 

 cycle of reproduction, the use of the term homologous 

 appears to indicate, at least, the general character of the 

 process, better than any other in common use. 



I have only, in conclusion, to repeat my regret, if the 

 spirit of system has in any respect given a false bias to the 

 interpretation of the facts of nature. Impressed, as I have 

 long been, with the conviction of the prevalence of an 

 orderly arrangement throughout the works of the great 

 Creator, who " hath made all things double one against 

 another ;" and, believing that some such guiding principle 

 has been successfully used by the most cautious explorers 

 of nature, as a clue to her more intricate mazes, I freely 

 admit having proceeded, in the examination of the com- 

 parative details of the process of reproduction, with a strong 



