212 University of California Publications in Zoology [Vol. il 



in the more rapid movements, yet the same whiplike motion 

 carries the body forward. 



Cessation of movement in the swimming reflex takes place 

 by a slowing up of the rhythmical movements, followed by 

 attachment of either the anterior or posterior sucker first, the 

 other one becoming attached immediately afterwards. In one 

 individual twenty-four swimming reactions were observed in 

 order to see which sucker was most often attached first. The 

 following are the results : Anterior sucker attached first, 19 

 times ; posterior sucker attached first, 5 times. This is to be 

 explained by the fact that the anterior end, being foremost in 

 locomotion, most often comes first in contact with the surface 

 upon which the animal comes to rest, or to attach itself and take 

 up the looping type of locomotion. 



In the species of Glossiphonia and Hcmidepsis studied, the 

 swimming reaction was not observed at all, no amount of stimu- 

 lation being successful in evoking this type of response. Both 

 of these species carry their young attached to the ventral surface 

 of their bodies. A special modification of structure accompanies 

 this mode of behavior, the body being so shaped as to form a 

 pouch-like cavity underneath the ventral surface, and it is evi- 

 dently due to this difference in structure that we have this corre- 

 sponding difference in behavior. Von Uexklill (1905) has de- 

 scribed the swimming movements in the blood-leech. Both the 

 blood-leech and the nephelids do not carry their young, but form 

 cocoons, much as the earthworm does. Thus it seems probable 

 from the forms studied that those groups of leeches which carry 

 their young are so modified thereby in structure as to be rendered 

 incapable of the swimming reflexes, while those that are not 

 encumbered with such a burden are provided with this freer and 

 more rapid mode of locomotion. 



5. Undulatory Respiratory IMovements 



When allowed to remain undisturbed in the aquaria for some 

 time, many of the leeches fix themselves by the posterior sucker 

 and exercise undulatory movements of the body. These are 

 much the same as the swimming movements already described, 



