in der Spongiologie während der Jahre 1897 und 1898. 305 



Phylogenie. 



Lendenfeld (4) hat Haeckels systematische Phylogenie der 

 Spongien (s. vorigen Jahresbericht) einer Kritik unterworfen, in der 

 er sich besonders gegen das von Haeckel aufgestellte System der 

 Spongien wendet; die Klasse der Malthospongien und die Legion 

 Pallactinella sind zu streichen. 



Die Phylogenese der Kalkschwammnadeln denkt sich Michin (3) 

 wie folgt: 1. The first appearence of a calcareous spicule or spicular 

 element, both ancestrally and in the actual development, was pro- 

 bably a minute vacuole in a cell of the dermal layer, filled with 

 on organic substance, perhaps indentical with the intercellular 

 ground substance, within the minute sclerite appeared as a 

 crystal or concretion. 2. The ancestral sclerite, though crystalline 

 in structure, soon assumed a non-crystalline form as a whole, 

 as an adaptation to its secondarily acquired function of support, 

 and as it grew in size the contents of the vacuole formed the 

 spicule sheath. 3. The ancestral form of spicule in the Calcarea 

 was a simple monaxon, placed tangentially and completely 

 embedded in the bodywall, lying between two adjacent pores. 

 4. From this ancestral spicule the forms of spicule now occuring 

 in the Calcarea arose as follows: (a) the primitive monaxon 

 acquired a distal portion projecting from the surface, as in the 

 existing primary monaxons; (b) groups consisting each of three 

 primitive monaxons became united by their contiguous ends to form 

 a Single triradiate System; (c) to some of the triradiate Systems 

 thus formed a fourth ray was added, secreted by the pore-cell; 

 giving rise to the quadriradiate System; (d) some of the trira- 

 diate Systems, by loss of one ray and placing of the other tw^o in 

 a straight line, or by loss of two rays, perhaps became modified 

 into secondary monaxon spicules. 5. The power of secreting 

 a monaxon sclerite was primitively possessed by every cell of the 

 dermal layer, and this condition appears to be retained in Leuco- 

 solenia. In Clathrina, on the other band, all the skeletogenous 

 cells migrate inwards from the dermal epithelium, and form a 

 connective-tissue layer distinct in function from the contractile, 

 undifferentiated dermal epithelium. In Leucosolenia also the 

 actinoblasts of the triradiate Systems form a deeper layer, but the 

 dermal epithelium secretes primary monaxons — at least in the 

 young form — and is non-contractile. 6. The forms of the spicules 

 are the result of adaptation to the requirements of the sponge as 

 a whole, produced by the action of natural selection upon Varia- 

 tion in every direction. 



Aich. f. Naturgeseh. Jahrg. 1894. Bd. H. H. 3 20 



