516 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



I am of opinion that this structure must be considered as an 

 organ of sense comparable to the ring nerve of craspedote Medusae 

 or the sensitive and ganglia cells, which form a circular zone in 

 the entoderm of the manubrium of certain hydroid polyps. 



The membrane surrounds, as mentioned above the lacunose 

 portion, and it is crowned by this nervous structure, which 

 accordingly appears as a sensitive zone round the askeletous area. 

 The distal swelling of the membrane consists of ganglia cells, the 

 nuclei of which are apparent, the limits of which however are 

 indistinct, there is only a slight indication of the formation of 

 limits. 



The spindle-shaped cells in the skin should be considered as 

 sensitive elements and their basal processes as nerves, which lead 

 from the sensitive cells to the ganglia cells. These processes are 

 short in the cells just above the ganglia cells and longer as the 

 cells are further removed. The tangental granular threads 

 represent tangental nerves which lead from the ring nerve to other 

 parts of the surface. 



This nervous system, as also that in other sponges, is meso- 

 dermal, and can therefore not be directly compared to the 

 analogous structures in higher Coelenterates, but as we find the 

 embryonic lamellae so very indifferent in these low animals no 

 great value can be attached to this difference. It is, however a 

 further illustration of the peculiarity of sponges first pointed out 

 by Marshall (1) that all their organs are mesodermal, that even 

 the nervous system which throughout the animal kingdom is 

 ectodermal or entodermal ( Hydroid polyps, Actinia), is constituted 

 of mesodermal cells in sponges. 



There can be little doubt that there is a connection between the 

 muscular cells of the membrane and the ganglia cells, although I 

 have not been able to ascertain what this connection may be. 



(1) W. Mamhall. Die Ontogenie von Reniera filigrana, 0. Schmidt. 

 Zeitschrift fiir wissenschaftliche Zoologie. Band XXXVII., Seit 497. 



