GRASPING ORGAN OF DENDROCOELUM LACTEUM 



377 



the grasping organ as seen in surface view, is well represented 

 in figure 2. It was with great difficulty that a planarian was 

 killed with the grasping organ extended, and the preparation 

 from which figure 2 was drawn was the only one in perhaps a 

 hundred to show the organ favorably. 



The organ consists of two ridges on the ventral side of the 

 head, which converge abruptly and meet as two thickened, club- 

 shaped lips at the anterior end. Posteriorly the ridges become 

 broad and low, and merge into the ventral surfaces of the head. 



Evidently this specimen was fixed in a condition of semi- 

 extension, for a transverse section of another Dendrocoelum 

 (fig. 3) shows the median groove to be greatly narrowed and 

 the ridges on either side to be folded together. 



mu. cr 



7im. crc.-->- 



^mu. Ig. 



Figure 3. Transverse section .of grasping organ showing musculature; mu. crc. 

 circular muscles; e'th. epithelium; mu. Ig. longitudinal muscles. Magnified 

 75 diam. 



There are no rigid structures to be discovered in sections of 

 the grasping organ. Such sections show an abundance of mus- 

 cular tissue (fig. 3). It would appear probable that the grasping 

 organ is extended through the action of these muscles upon the 

 body fluids, thus producing a pressure which would stretch the 

 anterior part of the ridges and perhaps give to the head an upward 

 turn, thus bringing the ventral ridges into an anterior position. 

 Figure 1, C and D, illustrate how this action may take place. 

 The movement is too quick to allow of very accurate analysis, 

 but it is evident from the way in which this organ is used and 

 from the structure as seen in figure 1, that it is more appro- 

 priately designated a grasping organ, than a sucker. 



