OBSERVATIONS OX FßE.-jH-WAl'EK POLYZOA. 91 



&ay about one in ei'.cli four «(^uure millimetres. The more centrally 

 situated polypides being older are the tirst to die, so that in old 

 colonies, th.', polypides are f(3und only on the outer part, leaving the 

 inner part bare and only marked with dark spots, the remains of dead 

 polypides. When agitated the polypides retract only for a short 

 time, and soon expand their tentacular crown again. Even in being 

 transferred from one vessel to another, some of the ])olypides of a 

 colony do not reti'act at all. In confinement, however, they seem 

 to become more timid and, once retracted, remain in that state for a 

 longer time than when free. 



Each colony originates from a single individual that comes out 

 of the statoblast in the first weeks of July, becomes larger and larger 

 by successive budding, attains its full growth in October, and 

 C(mtinues to live until the end of December. Compared with a 

 species of Plumatella living in the same pond, the times of the first 

 appearance and of the total disappearance are each about two months 

 later. As I have not found this species anywhere else, I can say 

 nothing about its geographical distribution. 



Methods of Investigation. 



Before proceeding further, I may here give a brief account of 

 the methods of investigation employed. To kill the animal in 

 a fully expanded condition was in this case very easy, although it is 

 the princij)al difficidty met with in the preservation of all other 

 genera. When 70% ^dcohol is gradually [)Oured into a vessel contain- 

 ing the colonies, more than half the ])olypides die protruded. If we 

 use such stupefying reagents as chloral hydrate or ccjcain chlorhydrate, 

 every one of the polypides dies in a fully ex[)aiKled condition. 



The colonies after being killed were put into alcohol to be hard- 

 ened. S(jme of them were fixed with a saturated solution of c<jrros- 



