46 HISTORY OF THE HUMAN BODY 



apparent to the early morphologists, one of the greatest of 

 whom thus expressed his feelings while gradually tracing back 

 from the adult condition the developmental history of the 

 skull of the common fowl : " Whilst at work I seemed to 

 myself to have been endeavoring to decipher a palimpsest, and 

 not one erased and written upon again just once, but five or 

 six times over. Having erased, as it were, the characters of 

 the culminating type, that of the gaudy Indian bird, I 

 seemed to be among the sombre Grouse; and then, towards 

 the end of incubation, the characters of the Sand-grouse and 

 Hemipod stood out before me. Rubbing these away, in my 

 downward work, the form of the Tinamou looked me in the 

 face; then the aberrant Ostrich seemed to be described in 

 large archaic characters; a little while, and these faded into 

 what could just be read off as pertaining to the sea-turtle ; 

 whilst, underlying the whole, the Fish in its simplest Myxinoid 

 form could be traced in morphological hieroglyphics." * 



In following out the historical development of the different 

 systems, as outline^ in the ensuing chapters, both embryonic 

 and phylogenetic records have been drawn upon as the primary 

 sources from which this history may be deduced, and the 

 conclusions which have the corroboration of both may be 

 naturally considered the most trustworthy ones. Each of these 

 two records has its advantages and its disadvantages ; in the 

 former the stages are continuous, although the early ones are 

 obscure, and all parts of the record are apt to be overlaid and 

 mystified by caenogenetic changes ; in the latter the record is far 

 1 more fragmentary and its stages are discontinuous, but the 

 facts are usually plainer and more easily read. An adult lower 

 animal which represents a phylogenetic stage in the history of 

 a higher shows the parts in full physiological efficiency, while 

 in an embryonic stage the organs are at the best not wholly 

 functional, and often render it difficult to imagine an adult 

 animal with the same relationship of parts ; on the other hand, 

 in places where a long historic period has no known living or 



* W. K. Parker, in Trans. Roy. Philos. Soc , 1869, pp. 803-804. 



