210 University of California Publications in Zoology [Vol. 11 



3. Looping Response 



The looping reaction is so designated on account of its resem- 

 blance to the movements of the Geometrid larvae or "measuring" 

 worms. Von Uexkiill (1905) describes this type of response 

 in the blood-leech as "das Gehen," preferring this term to 

 "Kriechen," because not all of the ventral surface of the animal 

 is in contact with the substratum, the suckers of the animal being 

 the parts of the body on which most pull is exerted. 



The circular muscles contracting antero-posteriorly, and the 

 longitudinal muscles extending, the anterior end of the animal 

 is pushed forward, the arch produced in the preceding crawling 

 movement serving as a leverage to assist the muscular action 

 more easily to push forward the anterior portions of the body. 

 Executing random movements and becoming oriented, the an- 

 terior end of the body, which serves as the anterior sucker, is 

 applied to the substratum. Antero-posterior contraction of the 

 longitudinal muscles now takes place, more rapidly than did their 

 extension, and in the nephelid the posterior sucker is drawn 

 along in contact with the surface without its being lifted from 

 the substratum. The posterior sucker is advanced only a portion 

 of the distance between its place of attachment and that of the 



a 



Fig. 2. — Looping responses: (a) of Bina microstoma; (6) of Glossi- 

 pho7iia stagnalis. 



anterior sucker in the case of Dina microstoma; in Glossiphonia 

 and Hemiclepsis it is u.sually placed closelj' against the anterior. 

 This difference is indicated in the accompanying figure (fig. 2, 

 a,h). In the latter two genera, with each loop, in many cases, 

 the posterior sucker is released from the substratum and placed 

 near the anterior, differing in this respect from the movements 

 of the nephelid. In Glossiphonia, however, the posterior sucker 



