Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College, No. 262 



THE GRASPING ORGAN OF DENDROCOELUM 



LACTEUM 



ELIZABETH S. P. REDFIELD 



The grasping organ of Dendrocoelum lacteum is situated on 

 the ventral surface of the anterior part of the head of this worm, 

 between its two auricular appendages. 



Ijima ('84) records this organ as used for locomotion against 

 currents. Gamble ('96, pp. 35-48) describes this species as 

 ' affixing a sucker, placed on the under side of the head, to 

 the substratum, and pulling the posterior end close to this. 

 The sucker, discovered by Leydig, is even better developed in 

 (Planaria) punctata, P. mrazekii, and P. cavatica, and is an 

 efficient adhering-organ, which has probably been developed 

 from a similar but simpler structure, found in a considerable 

 number of both fresh-water and marine Triclads." 



How far these interpretations apply to Dendrocoelum lacteum, 

 will appear in the following account. This paper is based on an 

 experimental study of the function of the grasping organ in 

 Dendrocoelum lacteum, and I wish to thank Dr. G. H. Parker, 

 under whom the work has been done, for his kind assistance. 



STRUCTURE OF THE GRASPING ORGAN 



The grasping organ of Dendrocoelum lacteum, when studied 

 under a low power of the microscope, appears as two symmet- 

 rically placed opaque thickenings, near the middle of the anterior 

 margin of the head. In the resting condition, these structures 

 project forward very slightly, forming a pair of rounded lobes, 

 as shown in figure 1, A. 



As the planarian moves about in ordinary locomotion, this 

 organ is in continual activity, stretching out, contracting, now 

 grasping an object, now rejecting it. When grasping at materials 

 these lobes are stretched forward fully twice their resting length 

 and press the object, one on each side (fig. 1, B). The form of 



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