BY R. VON LENDENFELD, PH.D. 983 



Ganglia cells have been observed in several of the species 

 mentioned above. They are highly colorable (particularly their 

 nucleus) multipolar cells. In Sycandra arborea they lie between 

 the muscular fibres of the Sphincter and the sensitive elements, just 

 above them. In Leucandra they are often found near the base of the 

 clusters of sensitive spindle-cells. 



They are here of the same shape as in Sycandra. 



Also in connection with the solitary sensitive cells of Leucandra 

 conica solitary Ganglia cells are found. Also these seem to be of 

 the same multipolar kind as in the former cases. 



THE ECTODERM, 



In all Calcareous Sponges the Ectoderm consists of simple pave- 

 ment cells, which cover the outer surface, the inhalent canals and 

 often also extend over the spicules protruding from the outer 

 surface. No differentiation of any kind can be detected. Many 

 of the cells are flat (on the surface) or concave (in the pore canals) 

 or convex (on the spicules), they always represent the same simple 

 type of low plates filled only partially with protoplasm, which 

 surrounds the compressed nucleus and adheres as a thick plate to 

 the outer surface. From this plate threads extend, which pervade 

 the cell cavity. 



The question whether the nervous and gland cells really are 

 Mesodermal, as I assume, or Ectodei'mal, seems worth discussing. 



My assumption of the Mesodermal nature of these organs is 

 mainly based on the fact that the Ectodermal Epithelium cells 

 never show any tendency of higher development. There exists 

 no transition forms between the pavement cells and gland or 

 nerve cells. Such transition forms do however exist in great 

 quantity between these elements and the indifferent, doubtlessly 

 mesodermal star-shaped tissue cells, from which, muscles and pro- 

 bably nerves have been differentiated ; whilst the gland cells may 

 possibly be referrable to another and more recent kind of meso- 

 derm cells, from which also the sexual cells originate the meso- 

 dermal wandering cells. 



