238 University of California Publications in Zoology [Vol. 11 



repeatedly attach themselves is also a feature iu their favor. lu 

 the absence of an adult form, the young collect in groups on the 

 bottom of the aquarium just as do the older specimens. In the 

 young of Hemiclepsis occidentalis this reaction is just as pro- 

 nounced as in those of Glossiphonia stagnalis, though I have not 

 collected the adults of this Hemiclepsis in groups such as Glossi- 

 phonia forms. It may be, however, that where they occur abun- 

 dantly the formation of collections may also take place in this 

 species. In one dish, forty-three young of Hemiclepsis were 

 placed, and these formed two groups which were not dispersed 

 during the two weeks in which the experiment was continued. 

 Any disturbance of the dish, such as jarring or blowing on the 

 surface of the water, caused a vigorous waving of the anterior 

 end of their bodies, as if they were searching for the disturbing 

 factor. 



A large specimen of Hemiclepsis occidentalis carrying the 

 forty-three young above mentioned was first separated from its 

 young. In the dish with these young of Hemiclepsis was placed 

 an adult Gl. stagnalis which formerly had been carrying young, 

 but from which this encumbrance had been removed sufficiently 

 long for the animal again to become normal in its movements. 

 After remaining in the dish eighteen hours with the young, these 

 several times being aroused to activity, this adult Glossiphonia 

 did not carry a single one of the young He^niclepsis. The orig- 

 inal parent was now placed in the dish, and within five minutes 

 two of the young had found their nestling place on the parent 

 Hemiclepsis. Twenty minutes later a total of eight was found 

 attached, the others having become massed along the sides of 

 the dish. 



The movements of the larger species, adult as well as young, 

 are somewhat slower than those of Glossiphonia, and it was 

 thought that here might be a possible explanation of the differ- 

 ence in the behavior of the young towards adults of two different 

 species. Two specimens of Glossiphonia were decapitated, and 

 necessarily, after a short time, little movement resulted. Al- 

 though the young of the larger species were kept moving actively 

 about the decapitated specimens, none attached itself to the body 

 of these leeches of a different genus. 



