THEORY OF RADICALS AND MORPHOLOGICAL EQUIVALENCE. 27 



sought by the animal or forced upon it by geologic changes. Professor Cope, 1 

 in his masterly work on the " Origin of the Fittest," and in pamphlets previously 

 published, described "homologous" and "heterologous" series equivalent to 

 what we have called homoplastic and homogenous series, and gives numerous 

 instances from all departments of the animal kingdom of exact and inexact 

 parallelisms sustaining the position taken above. This eminent author discusses 

 at length the location of growth force due to use or habits, and shows this to be 

 an efficient cause of modification, thus bringing out clearly and demonstrating 

 a new law of variation. His opinions with regard to "mimetic analogy" in 

 external and internal characters differs only in so far as we have preferred to use 

 the term morphological equivalence, because we thought it expressed more 

 exactly the phenomena of homoplasy. He says (p. 96), " I believe such coin- 

 cidences express merely the developmental type common to many heterologous 

 (homoplastic) series of a given zoological region.'' With regard to the effects 

 of habit, we should also refer to Cope's remarks (p. 198), and examples with 

 which he explains the origin of generic characters in the ossification of the 

 cranial walls in the Batrachia, and the origin of horns among Ruminants, as due 

 to habits of defence, concluding (p. 200) that the use of the angles of the parts in 

 question (the head) would result in a normal exostosis of a simple kind in the 

 frogs, or as horn cores in the Ruminantia. Waagen, in his " Jurassic Cephalopoda 

 of Kutch," a has made a valuable contribution to the facts in tracing several par- 

 allel series of Lytoceratinae in India and Central Europe. "The most important 

 facts which result from the investigations explained in the present volume are 

 these two : first, that in Kachh, in the same manner as in Europe, developmental 

 series exist, which are in part identical with the European ones ; and second, that 

 the succession of the identical species in time during the Jurassic period in Kachh 

 has been governed by exactly the same laws as have been observed in Europe." 



" For facts (parallel series 3 ) like those mentioned, which would be augmented 

 by a good many instances if other groups of Ammonites were as well known as 

 Phylloceras, the only explanation is, that the changes of form in the organic 

 world were dependent upon laws which were innate in them and had not to 

 rely exclusively on outer circumstances. The latter factors, as struggle for 

 existence, geographical separation, etc., certainly influenced the production of 

 forms greatly ; but the fundamental law upon which these influences acted very 

 likely was not the law of variation, as stated by Darwin, but the law of develop- 

 ment, or the tendency of the organisms to produce an offspring varying in a cer- 

 tain well defined direction. If this law be true, the time will come when we shall 

 be able to indicate a priori, with tolerable certainty, what species a given form 

 can or might produce." 



1 Origin of Genera, Proc. Acad. Nat. Science, 1863; Methods of Creation, Ibid., 1871, p. 229; and 

 Origin of the Fittest, p. 95 et seq. 



2 Paleontol. Ind., Juras. Fau. of Kutch, I., Ceph., pp. 212, 243. 



3 Waagen's parallel series end in the evolution of identical forms or species from or through different 

 species. We have never met an example of this kind which did not admit of explanation as the result of 

 migration. Waagen's remarks, however, apply to parallel series in general, whether the forms ultimately 

 evolved are the same, or merely resemble one another more or less closely. 



