246 University of California Publications in Zoology [Vol. 11 



alive and in good condition for six naonths. No perceptible signs 

 of regeneration appear in any of the individuals, neither the 

 anterior nor the posterior end regenerating new segments. No 

 sections of the leeches have been made to determine to jnst what 

 extent regenerative processes have taken place. Not all of the 

 specimens operated upon have survived for as long as six months, 

 the mortality being approximately seventy-five per cent. The 

 wounds of the surviving specimens have in practically every case 

 entirely healed over. What the result of such operations might 

 be upon subsequent regeneration in young Dinas is a matter of 

 uncertaintJ^ The work of Gluschkiewitseh (1907) is certainly 

 suggestive in this regard. 



Wlien approximately the first eight anterior segments are 

 removed from the body of Dina microstoma, the operation has 

 the effect in most cases of setting the animal to swimming vigor- 

 ously about in the dish. After a short period, the decapitated 

 specimen settles to the bottom, becoming attached by the posterior 

 sucker, the body stretched along the bottom of the dish. Except 

 for a slight occasional movement of the anterior end, here it may 

 remain for many hours. 



A slight stimulation of the posterior end of such an animal 

 produces an unequal contraction of the dorsal and ventral longi- 

 tudinal muscles of the body, causing the leech to become arched, 

 and its anterior end to be pressed against the bottom of the dish. 

 Since the anterior sucker is not present, progressive movement 

 cannot be made effectively by looping ; so the muscles are relaxed, 

 and the body assumes its previous position. In some cases, the 

 pressure of the anterior end against the substratum affords suffi- 

 cient leverage for the animal to drag its posterior sucker forward 

 a short distance. This would seem to indicate that the mechanism 

 for forward movement by looping is present except for the an- 

 terior sucker. The lack of this produces a clumsiness of response, 

 but the reflexes constituting the movements of this type are all 

 present in the decapitated specimens. The reaction of the decap- 

 itated specimens to an average stimulus is usually the swimming 

 reflex. This is performed in a perfectly co-ordinated manner, 

 though the blunt anterior margin forms not nearly so efficient 

 a steering agent as does the attached graceful anterior end. 



