and the Theory of Descendence. 429 



4. The extremely remarkable conditions of the intercanal 

 system are brought about merelj by concrescence. By this 

 purely mechanical process of growth very complicated and 

 characteristic stock-forms and personal forms are produced, in 

 which enclosed 2)ortions of the sea become constituent organs of 

 the organism. 



5. The exceedingly characteristic primary /or Hi of the cal- 

 careous sjncida is a purely mechanical ])roduct of two co- 

 operating factors, the cajyaciiy for crystallization of calc-spar 

 and the secretory activity of the sarcodine. In the production 

 of the secondary forms of spicules the formative current of 

 water and adaptation to other, more subordinate, external 

 conditions of existence are efiective. 



6. The orderly, often very regular, elegant, and apparently 

 artificial constitution of the skeletal system is for the most part 

 a direct product of the current of loater ; the characteristic 

 position of the spicules is produced by the constant direction of 

 the current of water ; to a very small extent it is the con- 

 sequence of adaptations to subordinate external conditions of 

 existence. 



7. All other characters of form which might come into con- 

 sideration here may be referred to the formative activity of the 

 cells of which the two constituent lamellaj of the sponge-body, 

 the entoderm and the exoderm^ are composed ; but tbese are 

 inherited from the Protascus, and further from the Gastrcea. 

 The motile phenomena of these cells are particularly efficacious 

 in this respect — on the one hand the amoeboid movement^ and 

 on the other the flagellar movement, which is to be referred to 

 the latter. 



8. The special properties of these cells in the Calcispongise 

 are due to the chemical conq?osition of their body — of the pro- 

 toplasm on the one hand and of the nucleus on the other. Of 

 these two constituents of the cell, the protoplasm is especially 

 to be regarded as tlielnorgan of adaptation, and the nucleus as 

 the bioryan of inheritance. 



9. The (chemical) properties of the two albuminoid com- 

 pounds which form the protoplasm and the nucleus are to be 

 referred to the peculiar affinities of carbon. Originally they 

 were active in the simplest manner in the constitution of the 

 jylasson which formed the entire body of the simplest Moneron. 

 From this was produced, only by adaptation (differentiation of 

 the plasson into nucleus and protoplasm), the first cell, an 

 Amoeba. This is recapitulated, in accordance with the bio- 

 genetic fundamental law, by the ovicell. The specific pro- 

 perties which the ovicell of the Calcispongije possesses were 

 acquired by it by inheritance from the most ancient Olynthus. 



