1913] Gee: Behavior of Leeches 215 



ease, when dropping through the water, and approximately the 

 mid-dorsal surface comes in contact with the bottom of the dish, 

 the response is a muscular movement, straightening the body 

 and turning it towards the side on which the center oi gravity 

 happens to lie. Either the anterior or posterior sucker may be 

 attached first, the body then being twisted over into its proper 

 position. 



The righting process is iLsvially accomplished with the aid of 

 the suckers. Sometimes, however, it may be performed by the 

 swimming reaction being given, the specimen orienting its body 

 properly by the steering action of the anterior end. Loeb (1894) 

 noted in regard to the righting reaction of blood-leeches which 

 had been operated upon : ' ' Legt man das hintere Stiick auf 

 den Riicken, so beginnt es Schwimmbewegungen zu maehen, 

 dnrch welche es sieh in die Bauehlage zuriickbringt. Das vor- 

 dere Stiick erreicht die Bauehlage durch direktes Umwenden." 

 In the species of Dina, where the posterior three-quarters of the 

 body has been removed, the righting is, as Loeb has described it 

 for the blood-leech, by a direct turning. The anterior sucker 

 is attached and the body turns toward the side on which the 

 center of gravity happens to fall. In the posterior portion, 

 when the anterior sucker has been removed, the responses to 

 reversed position of the body may be swimming, and the righting 

 may take place during this process. Often, however, the response 

 is a direct turn, as in the anterior portion. The posterior sucker 

 inclines toward the substratum, becomes attached, and turns the 

 animal, aided by the leverage derived froni the pressure of the 

 anterior end against the bottom of the dish. Even a section a 

 few millimeters in length removed from the middle region of 

 the body will right itself through a contraction of the dorsi- 

 ventral muscle exerting a pull toward the ventral side and thus 

 turning the body over to its normal position. 



The righting reaction in Glossiphonia is more stereotyped 

 than in Dina microstoma. It is usually accomplished by the 

 attachment of the anterior sucker and a twisting pull is exerted, 

 much as Pearl (1903) has described in the planarian, by means 

 of which the body is turned into its proper position. The pos- 

 terior sucker is brought close to the anterior and the leech loops 

 forward. 



