260 Prof. E. Hackel on the Position of the 



The comparative anatomy and developmental history of the 

 Calcispongiaj furnish a coherent confirmation of this principle. 

 Supported upon this, we have been enabled in the preceding 

 pages to attempt to extend their consequences beyond the 

 narrow domain of the Sponges to the general phylogeny of 

 the animal kingdom. We are induced to indicate it expressly 

 here once more, partly by the opposition which our biogenetic 

 principle has met with*, and partly by the desire to recall 

 certain guiding principles which have come up with reference 

 to ontogeny on this occasion. 



The newer ontogeny or embryology has evidently fallen 

 from year to year more and more into a chaos of contradictory 

 opinions and assertions, which show the value of this science 

 in a very doubtful light. We need only refer to the perfectly 



* The most decided opposition to the biogenetic fundamental principle 

 has been raised by the embryologist Professor His, of I^eipzig (Ueber die 

 erste Anlage des Wirbelthier-Leibes : Leipzig, 18(37 ; and Ueber die Be- 

 deutung der Entwickelungsgeschichte fiir die Auffassung der organischen 

 Natur: Leipzig, 1870). The views as to the significance of ontogeny 

 which His here develops stand in the most absolute antagonism to 

 mine ; but it can only be for the advantage of the advance of knowledge 

 that such irreconcilable contradictions should be expressed as clearly and 

 distinctly as possible. Eitlier there is or there is not a direct and causal 

 connexion between ontogeny and phyloc/eny. Either ontogenesis is a con- 

 densed (and partially masked by adaptation) abstract of phylogenesis, or 

 it is not. His holds the latter opinion ; I hold the former. In my opinion 

 Ilis, in his antagonism to phylogeny, stands entirely on the ground of the 

 long-since exploded evolution-theori/, although he seems to attack it. He 

 has not at all comprehended the true theory of epigenesis ; otherwise he 

 would have understood its intimate connexion with the descendence- 

 theory ; for the two are inseparable. As regards the much-admired 

 attempts of His to explain ontogenetic facts after a new, jirofessedly 

 mechanical fashion, these seem to me quite erroneous and valueless. 

 The attempt to conceive of the germinal disk (which is not elastic ! ) as 

 an elastic plate, and to explain by its unequal extension the production of 

 the folds — the attempt to explain the homology of the four extremities of 

 the Vertebrata by the crossing of four folds circumscribing the body, like 

 the four corners of a letter, and other similar fancies, appear to be 

 susceptible only of a humorous examination, but not of serious refutation. 

 That these droll fancies should have been admired as great ideas proves 

 the complete want of j udgment which at present prevails both in ontogeny 

 and histology. At the same time, however, these great errors, with 

 respect to which we can only regret the great expenditure of time, trouble, 

 and industry that they have cost, show how necessary for investigations in 

 the difficult field of ontogeny is orientation in the domain of comparative 

 anatomy, and reference of ontogenetic processes to their mechanical phylo- 

 genetic causes, their true " cansee efficientes." Only because these two 

 conditions are not fulfilled by His can we explain how he could arrive 

 at so completel}^ erroneous a conception of embryology. It is true that 

 Uonitz (following the example of his master, Reichert) has shown that 

 the confusion in the domain of ontogeny can be carried much further, 

 and that even the g:erm-lamella theorv is no longer necessan'. 



