428 Prof. E. Hackel on the Calcispongige 



The most remarkable form of polymoi'phosis among the 

 Calcispongia3 is the union of polymorpliotic persons upon one 

 stock, which I have called metrocormism. In the artificial 

 system these metrocorviotic Calcispongim form the order of the 

 Metrograntiaj {Ascometra, Leucometra, Sycometra). Forms 

 which the artificial system regards as representatives of dif- 

 ferent genera and species here grow united upon a single stock. 

 This fact is quite irreconcilable with the species-dogma. 



5. Causes of the Production of Form. 



Besides the great interest which the biology of the Calci- 

 spongiffi possesses in connexion with the theory of descendence 

 and the critical conception of the organic species, it is also of 

 extraordinary general significance, because in this small and 

 simply constructed group of animals the true causes of biological 

 phenomena, and especially the causes of the production of form, 

 may be reviewed with particular clearness and recognized with 

 particular certainty. These causes prove throughout to be 

 purely mechanical unintelligent causes [causxe efficioites), while 

 we seek in vain for any designedly active intelligent causes 

 {caus(B finales) . 



If Ave briefly sum up the most essential points relating to 

 this matter, we arrive at the following results : — 



1. The general external form of the Ccdcisjjongia' , both that 

 of the social stocks and that of the individual j)&^' sons, is a pro- 

 duct of growth which is principally governed by adaptation to 

 the external conditions of existence of the locality and surround- 

 ings ; the mode of growth is only to the smallest extent in- 

 herited within the species. The same applies to the quadruply 

 ^i&tYQni formation of the mouth in the persons. 



2. The triply different structure of the loall of the stomach by 

 which the three natural families are distinguished is in part a 

 product of inheritance and in part of adaptation. The original 

 structure of the wall of the stomach, as it occurs in the Ascones, 

 is inherited from Olynthus, the stock-form of all Calcispongias : 

 Olynthus, however, inherited it from the Archispongia, the 

 latter from the Protascus, and this from the Gastrcea. The 

 structure of the wall of the stomach in the Leucones has been 

 produced from that of Olynthus by growth of the exoderm and 

 stabilization and ramification of the inconstant pores, and the 

 structure in the Sycones by strobiloid budding. 



3. The multifarious other characters of the gastro-canal 

 system are mere products of special adaptations, in which the 

 floio of water is especially effective ; this, again, is dependent 

 on the movement of the flas-ella of the cells of the entoderm. 



