Wilder.] 338 [June 21, 



ture and relative position, and I quote a few passages: " There ex- 

 ists, doubtless, a close general resemblance in the mode of develop- 

 ment of homologous parts; but this is subject to modification, like the 

 forms, proportions, functions, and very substance of such parts, with- 

 out their essential homological relationships being thereby obliterated. 

 These relationships are mainly, if not wholly, determined by the rel- 

 ative position and connection of the parts, and may exist independ- 

 ently of form, proportion, substance, function, and similarity of 

 development. But the connections must be sought for at every 

 period of development, and the changes of relative position, if any, 

 during growth, must be compared with the connections which the 

 part presents in the classes' where vegetative repetition is greatest - 

 and adaptive modification least" (20, 174). " So far is embryology 

 from being a criterion cf homology" (63, 1. xxvi). "Embryology 

 affords no criterion between ossific centres that have a homological, 

 and those that have a teleological significance" (63, 1, xxv). "No 

 part is, however, absolutely autogenous throughout the vertebrate 

 series, and some parts usually exogenous are autogenous in a few in- 

 stances " (63, 1, 27). "The developmental phenomena of the head 

 neither supersede nor can supply the better evidences of homology 

 afforded by relative position and connections, any more than do 

 those of the foot ; ... it is neither here nor elsewhere the cri- 

 terion of homology " (63, 2, 311). Cleland says, "Morphologically, 

 it is of little importance whether cranial bones are developed in the 

 primordial cartilage of the skull or around it " (215, 305). 



The general importance of embryology in the determination of ho- 

 mologies has been urged by Goodsir and Huxley, and in 251 the lat- 

 ter has well indicated the necessity of deciding the general question 

 before attempting to solve minor problems respecting the correspond- 

 ence of the skull and the vertebral column. Agassiz has constantly 

 presented the taxonomic value of embryology not only throughout 

 his later works, but in the lectures on Comparative Embryology, 

 Boston, 1849; and upon the ground of a difference of development, 

 he in great measure bases his opinion that the Batrachians form a 

 class distinct from the scaly reptiles ; but in discussing this, Dana 

 asks 1 " whether, in the determination of classes it is not the more 

 correct method to take note primarily of species in their finished or 

 adult state ; and whether adults do not express the true nature and 

 idea of species, or the objects to be classified, rather than the special 



i Am. Journ. of Sci., Mar. 1864, p. 184. 



