PRESENT TENDENCIES OF MORPHOLOGY 267 



of organic type, so important as we have come to see, has been 

 obscured for a long time by the imperfection of our knowledge con- 

 cerning individuality or rather concerning individualities of differ- 

 ent orders. Among the composite animals especially, such as the 

 sponges, the hydroids, the bryozoa, the synascidians, we have for 

 a long time attributed an exaggerated taxonomic value to the 

 cormogenesis, that is, to the mode of grouping of the individuals, 

 while neglecting the real relations of kinship that the anatomy of 

 these individuals reveals. It is not the least service rendered by 

 E. Haeckel to biological science that he first attempted to fix the 

 rules of this branch of morphology, which is like the architectonics 

 of living beings and which has been called tectology. Especially 

 among the metazoa, the tectological idea of the person, that is to 

 say, of the original diblastic being (gastrula) which constitutes the 

 most common mode of individuality, is an acquisition of inestim- 

 able value. 



Foreseen by de Blainville and by Huxley, who deduced it from 

 purely anatomical considerations, this idea was clearly established by 

 Haeckel as early as 1872, thanks especially to the admirable embryo- 

 logical investigations of Alexander Kowalevsky, investigations which 

 proved the existence of the gastrula larva in all the groups of multi- 

 cellular animals in which the development is explicit. 



Despite the recent attacks to which it has been subjected, the 

 theory of the gastrula, properly understood, is established as surely 

 as that of the homology of the blastodermal layers which is the 

 immediate consequence of it. 



The rational application of the principle of Fritz Miiller is suf- 

 ficient to account for the difficulties offered by certain condensed or 

 coenogenetic developments and the objections presented by some 

 authors who often hold to that which they have studied in only a very 

 small number of types (sometimes one unique type) , chosen by reason 

 of practical convenience and without regard to the disturbances of 

 ethological factors to which these types were subjected. 



The idea of an original form common to species but often pro- 

 foundly modified by the influence of environment renders evident the 

 folly of basing comparisons upon promorphology solely that kind 

 of crystallography or geometry of living beings. 



Such groups as those of the Radiaria or Radiata, the Bilateralia, 

 etc., are purely artificial and inspired solely by the idola promorpho- 

 logica. 



The truth remains, however, that it would be very desirable to 

 pursue further than has been done at the present time the promor- 

 phological studies of which Haeckel has furnished the basis in his 

 admirable general morphology. In this respect, as in many others, 

 morphology is directly dependent on geometry and mechanics. There 



