THE THREE-FOLD PARALLELISM 255 



parallelism Haeckel merely resuscitated in an evolutionary 

 form a doctrine widely discussed in the 'forties and 'fifties, 1 

 and championed particularly by L. Agassiz, 2 a doctrine 

 which must be regarded as a development or expansion of 

 the Meckel-Serres law. 3 It is the view that a parallelism 

 exists between the natural system, embryonic develop- 

 ment, and palaeontological succession. Actually, as Agassiz 

 stated it, the doctrine applied neither to types, nor as a 

 general rule to classes, but merely to orders. It was well 

 exemplified, he thought, in Crinoids : " The successive 

 stages of the embryonic growth of Crinoids typify, as it 

 were, the principal forms of Crinoids which characterise 

 the successive geological formations. First, it recalls the 

 Cistoids of the palaeozoic rocks, which are represented in its 

 simple spheroidal head ; next the few-plated Platycrinoids 

 of the Carboniferous period ; next the Pentacrinoids of the 

 Lias and Oolite with their whorls of cirrhi ; and finally, when 

 freed from its stem, it stands as the highest Crinoid, as the 

 prominent type of the family in the present period" (p. 171). 

 The Meckel-Serres law, it will be remembered, expressed 

 the idea that the higher animals repeat in their ontogeny 

 the adult organisation of animals lower in the scale. 

 Since Haeckel recognised clearly that a linear arrange- 

 ment of the animal kingdom was a mere perversion of 

 reality, and that a branching arrangement of groups more 

 truly represented the real relations of animals to one 

 another, he could not of course entertain the Meckel-Serres 

 theory in its original form. But he accepted the main 

 tenet of it when he asserted that each stage of ontogeny 

 had its counterpart in an adult ancestral form. Such 

 ancestral forms might or might not be in existence as 



1 See Vogt, Embryologie des Salmones, p. 259, 1842, and supra, p. 230. 



2 An Essay on Classification, London, 1859. 



3 It was hinted at by Tiedemann. " It is clear that, proceeding from 

 the earlier to the more recent strata, a gradation in fossil forms can be 

 established from the simplest organised animals, the polyps, up to the 

 most complex, the mammals, and that accordingly the animal kingdom 

 as a whole has its developmental periods just like the single individual 

 organism. The species and genera which have become extinct during 

 the evolutionary process may be compared with the organs which dis- 

 appear during the development of the individual animal'' (p. 73, i8o8j. 



