Reactions of Sponges 27 



flesh of the sponge is contractile is not without modern support. 

 Merejkowsky ('78, p. 14) states that if Suberites is so placed 

 that it is partly out of water, it will curve the body until it is 

 underwater as much as possible, and if the body is then 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 our of water quickly assume a shriveled and 

 rugose appearance as though the flesh had contracted on a resist- 

 ant skeleton, a condition which 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 

 appearance on being placed in running water. 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 seen well 

 around some of the larger cavities, such as the gastral cavity. If 

 a long finger of Stylotella w^hose two ends have been cut off^ and 

 whose gastral cavity extends along one of its sides is placed in 

 quiet seawater, the gastral cavity is soon indicated by an external 

 groove due to the apparent collapse of its wall. This groove, how- 

 ever, is caused not bv collapse, but by the contraction of the com- 

 mon flesh which as partial partitions or even travecula is abundant 

 about the sides of the gastral cavity- On returning the finger to 

 running water the flesh relaxes and the groove mostly disappears. 



Although the common flesh of Stylotella is unquestionably con- 

 tractile, I have never observed that the body of this sponge as a 

 whole moves in consequence of this contractility. Thus in no 

 instance have I seen a partly immersed finger of Stylotella bend 

 farther into the water, though I have let fingers stand in a posi- 

 tion favorable for this for over a day. Nor have I ever observed 

 fingers to turn in conformity to the direction of the current. Thus 

 some fingers of Stylotella are not directed straight upward, but 

 have their tips turned to one side or the other, so that the oscula 

 open laterally. A number of these were set, some with oscula fac- 



