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. 
leisy Is Ue 
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, ete. Structurally they have the appearance of a primitive 
Fig. 3. STRUCTURES FROM SPONGES. A. Dermal membrane of a sponge seen 
from the exterior. Membrane pieréed 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, (7). 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. 
