262 ERNST HAECKEL AND CARL GEGENBAUR 



fact is of great importance, for those changes \vhich an organ 

 undergoes during its individual development lead through 

 states which the organ in other cases permanently shows, 

 or at the least the first appearance of the organ is the 

 equivalent of a permanent state in another organism. If 

 then the fully developed organ is in any special case so 

 greatly modified that its proper relation to some organ-series 

 is obscured, this relation may be cleared up by a knowledge 

 of the organ's development. The earlier state indicated in 

 this way enables one to find with ease the proper place for 

 the organ and so insert it into an already known series. 

 The relations which we observe in an organ-seriation are 

 then the equivalent of processes which in certain cases take 

 place in a similar manner during the individual development 

 of an organ. Embryology enters therefore into the closest 

 connection with comparative anatomy. ... It teaches us to 

 know organs in their earliest states, and connects them up 

 with the permanent states of others, whereby they fill up the 

 gaps \vhich we meet with in the various series formed by the 

 fully developed organs of the body" (pp. 6-7). 



This recognition of the parallelism between comparative 

 anatomy and embryology is, of course, the kernel of the 

 Meckcl-Serres law. For Gegenbaur it had a very definite 

 evolutionary meaning he subscribed to the evolutionary 

 form of it, the biogenetic law. How near his conception of 

 the relation between ontogeny and phylogeny came to the 

 old Meckel-Serres law may be gauged from the following 

 passage, taken from a later work: "Ontogeny thus 

 represents, to a certain degree, palaeontological development 

 abbreviated or epitomised. The stages which are passed 

 through by higher organisms in their ontogeny correspond 

 to stages which are maintained in others as the definitive 

 organisation. These embryonic stages may accordingly be 

 explained by comparing them with the mature stages of 

 lower organisms, since we regard them as forms inherited from 

 ancestors belonging to such lower stages" 1 (p. 6). 



It is worth noting that in Gegenbaur's opinion compara- 



1 Grundriss der vergl. Anatomic, 1874, 2nd ed., 1878. Trans, by 

 F. Jeffrey Hell, revised by E. Ray Lankester, as Elements of Comparative 

 Anatomy, London, 1878. 



