CLASSIFICATION OF THE PRIMORDIA 81 



quantitative knowledge of the parts may enable us to analyse 

 the whole system. In this way a Morphology of the states of 

 equilibrium may be built up : this is, of course, only possible 

 by comparing numerous species. 



The resemblances which exist between the fruits of several 

 Myxomycetes may be brought under the principle of mechanical 

 concordance, in order to distinguish them from the morpho- 

 logical homologies. 



It may be expected that a morphology of the states of equi- 

 librium, based upon the quantitative investigation of the 

 primordia, may throw new hght not only upon the structure of 

 the above-mentioned plants, but also upon numerous resem- 

 blances to which the morphologists have hitherto paid Uttle 

 attention. 



EXAMPLES : A remarkable resemblance exists between the fruits of certain 

 Myxomycetes and that of certain Gasteromycetes {Lycoperdon, Tulostoma, 

 etc.). Both groups of objects are widely different in their phylogenetic origin, 

 their individual development and their morphological significance. For the 

 Gasteromycetes we may follow the embryological method, starting from an 

 initial cell and proceeding step by step till the adult state is reached. This 

 method, however, does not afford a complete elucidation of the final state of 

 equilibrium. The resemblance with the Myxomycetes remains unexplained, 

 because the embryological method is not applicable on the latter plants. As 

 long as we are influenced by the idea that morphological facts are merely 

 an expression of genealogical relations and may be completely elucidated by 

 embryology, the resemblances alluded to are a remarkable something, without 

 further significance. But when we look upon the objects mentioned as being 

 states of equilibrium, a new basis of comparison may possibly be obtained. 



Let us recall the striking similarity between certain Polyps (Campanularia, 

 Seytularia, etc.) and certain plants with regard to the relative position of the 

 branches ; the resemblance between the epidermic scales of many reptiles, 

 the dermic scales of many fishes and even the cuticular scales of butterflies 

 with regard to their relative position ; the astonishing resemblance between the 

 seeds of Drosera and those of many orchids ; the well-known so-called analogy 

 between the fore-legs of Gryllotalpa and Talpa, between the eye-shaped spots 

 which adorn the feathers of certain birds, the wings of certain butterflies and 

 the skin of certain fishes, etc., etc. 



In all similar cases, we try to explain the observed facts by means of the 

 principle of converging adaptation (which is based, at least in part, upon 

 physiological analogy). This principle involves a number of hypotheses. 

 Adopting the theory of natural selection, we are compelled to accept that : 



(i) The observed similarities have been brought about gradually, by the 

 accumulation of a long series of impalpable variations in each of the com- 

 pared species. 



(2) TTiese variations have been hereditary. 



(3) Each successive step has been the cause of certain advantages in the 

 struggle for existence, important enough to bring about the selection (survival ) 

 of the varying specimens. 



(4) The successive changes have been accumulated along the same line in 

 forms of life which difier from each other as deeply as a Myxomycet from a 

 Gasteromycet, a butterfly from a fish, etc. 



If we adopt the neo-Lamarckian theory, we must suppose that : 



(i) Each of the observed resemblances is the result of individual adaptations 

 (accommodations) to similar physiological functions or conditions of existence. 



(2) The variations produced by accommodation (in widely different species) 

 have been fixed by heredity. 



All the above hypotheses require verification. As long as this has not been 



