SPONGES 



13 



III. The Sponges 



The only activities of sponges which are in any way suggestive 

 of sense organs or a nervous system are those connected with the 

 water currents which enter and leave. 



The currents are caused by collar cells distributed in the vari- 

 ous chambers. These flagellate cells cause the continuous move- 

 ments of the liquids under ordinary conditions. The flagella of 

 these cells are connected with basal granules or blepharoplasts in 

 each case and in some, connections are also made with the nucleus. 

 Fig. 3, I, J. 



Lendenfeld, 1885-7, has described sensory cells and ganglion 

 cells in sponges, Fig. 3, E, F, G, but Minchin, 1900, and others 

 believe there are no true nervous elements. No modern work has 

 suggested the possibility of nerve cells or sense cells in Porifera. 



Parker, in 1910, describes elongated spindle-shaped cells ar- 

 ranged like irregular sphincters around the gastral cavity, oscu- 

 lum, etc. Structurally they have the appearance of a primitive 



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FiR. 3. 



Structures from sponges. A. Dermal membrane of a sponge seen 

 from the exterior. Membrane pierced by six pores, three of which are 

 partly closed by pore membranes. After Wilson, after Parker. B, C, 

 D. Three stages in the closure of the membrane pore. After Wilson, 

 after Parker. E, F, G. Sense cells and nerve cells, (?). After von 

 Lendenfeld. H. Two stages in the development of a muscle cell as the 

 first stage in the development of the nervous system. Diagram after 

 Parker. I, J. Collar cells from sponges. After Robertson, x 1,000. 

 K. Transverse section of the base of an oscular collar of a sponge 

 showing the cavity surrounded by a sphincter of myocytes, spicules 

 outside. Modified from Parker. 



