SPONGES 27 



covered with water, it will return to its former position. 



It must be evident, from what has already been stated, 

 that much of the common flesh of Stylotella is contractile. 

 As already noted, specimens out of water quickly assume 

 a shrivelled and rugose appearance as though the flesh had 

 contracted on a resistant skeleton, a condition that it also 

 quickly assumes in quiet seawater. Moreover, if a sponge 

 is placed partly in running seawater and partly in the 

 air, the portion in the seawater remains smooth and that 

 in the air becomes rugose. Specimens made rugose either 

 in the air or in quiet water soon recover their smooth ap- 

 pearance on being placed in running seawater. Air or 

 quiet water may then cause a contraction of the common 

 flesh of Stylotella, a condition counteracted by running 

 water. 



The contraction of the common flesh can also be well 

 seen around some of the larger cavities, such as the clo- 

 acal cavity. If a long finger of Stylotella, whose two ends 

 have been cut off and whose cloacal cavity extends along 

 one of its sides, is placed in quiet seawater, the cloacal 

 cavity is soon indicated by an external groove due appar- 

 ently to the partial collapse of the cavity. This groove, 

 however, is caused not by collapse, but by the contraction 

 of the common flesh which, as partial partitions or even 

 trabeculaB is abundant about the sides of the cloaca. On 

 returning the finger to running water the flesh relaxes and 

 the groove mostly disappears. 



Although the common flesh of Stylotella is unques- 

 tionably contractile, the body of this sponge has never 

 been observed to move as a whole in consequence of this 

 contractility. Thus in no instance did a finger of Stylo- 

 tella when partly immersed in seawater, bend farther into 

 the water, though fingers have been allowed to stand in 



