BY R. VON LENDENFELD, PH.D. 517 



The nervous elements of sponges have been developed from 

 neuio-muscle cells or also from indifferent mesodermal cells, the 

 former is rendered more probable by their distribution. 



The elements of sponges are derived from the different 

 embryonic layers as follows : — 



Ectoderm : 

 Flat Ejntliel cells. 



Entoderm : 

 Flat Epithet cells. 

 Collar cells. 



Mesoderm : 

 Tissue cells. 

 Flat Endothel cells. 

 Ova. 



Spermatoblasts. 

 Aiuceboid wandering cells. 

 Spongohlasts. 

 Gland cells of the skin. 

 Muscle cells. 

 Ganglia cells. 

 Sensitive cells. 

 The developement of the different Mesodermal cells may have 

 been the following : 



1 . The amoeboid wandering cells have retained the appearance 



and mode of life of those cells which originally grew 

 inward from the outer coating of the Blastula to form 

 the mesoderm. 



2. From these the ova, spermatoblasts and indifferent tissue 



cells have been derived ; also the Spongoblasts and gland 

 cells of the shin have descended directly from them. 



3. From the indijferent tissue cells neuro-niuscular elements 



were developed, which again further differentiated to 

 form the ganglia and sensitive cells on the one hand, and 

 the true muscular cells on the other ; also the connective 

 ordinary tissue cells are derived from them. 



