6 G. H. Parker 



chimnev-like projection. When contracted they are completelv 

 closed and the delicate tissue about them is puckered into a slight 

 spine-like elevation, the point of which represents the real position 

 of the osculum. The largest oscula when fully open measure, 

 as already stated, about four and a half millimeters in diameter. 

 From each osculum a branched gastral cavity extends through 

 the substance of the sponge either down the length of a finger or 

 into the massive body, depending upon the position of the oscu- 

 lum. In the fingered forms the gastral cavities lie either near 

 the axis of the fingers, and are thus buried in the substance of the 

 sponge, or on the surface of the finger, in which case they can be 



Fig. 2. Radial portion of a transverse section of Stylotella; the flesh of the sponge is tinted, the 

 cavities are untinted; on the extreme left is the dermal membrane pierced by two ostia that lead into 

 a large subdermal cavity, from which incurrent canals lead to the flagellated chambers, which in turn 

 open by an excurrent canal into the gastral cavity at the extreme right. X 25. 



traced*on the outside as translucent-walled canals well down 

 the length of the finger. Excepting the regions where the gastral 

 cavities show from the outside, the whole external surface ot the 

 sponge is faintly rugose and of a dirty-yellow color. 



Th einternal structure of the sponge is well seen in a transverse 

 section of a finger. On the outside of such a section (Fig. 2) is 

 a well defined membrane pierced in many places by dermal 

 pores or ostia. These openings are roundish or oval in outline 

 and, as seen in living bits of membrane torn from the outer surface 

 of the sponge, they measure from ten to tw^enty micra in diameter. 

 The ostia lead into relatively large sub-dermal cavities, which 



