212 
wide distribution within the class of the hydroids and therefore to 
be a character without any systematic value. 
Mereschkowsky (1878) has seen the spontaneous fission 
in "Obelia flabellata" (—= Laomedea longissima) and describes 
the process in accordance with Allman. 
During the following 26 years nothing has been published about 
the matter, until Billard (1904) wrote his large and interesting 
paper on stolonisation, fission, regeneration, grafting etc. in hydroids. 
— At this occasion I shall only mention the phenomenon, which 
he designates as "scissiparité sécondaire avec propagules simples", 
observed by Billard in the following species: Laomedea longissima, 
Laomedea geniculata, and Leptoscyphus tenuis (fscissiparité avec 
propagules complexes" was observed in Laomedea angulata, Hal- 
ecium sessile and Plumularia halecioides). — In a later note 
(Billard 1911) the same author has described a case of spont- 
aneous fission in Perigonimus repens. 
"One more case has been mentioned in the litterature by Hal- 
lez (1905) who saw the formation of frustules of the usual shape 
as one of the various results of some experiments carried out with 
«Obelia flabellata". These experiments will be further mentioned 
below. 
For the sake of completeness I must still mention that two 
German authors, Miller (1913) and Joseph (1913) have obs- 
erved double hydranths in various athecate hydroids. They are of 
the opinion, that such duplication may result in a complete longi- 
tudinal fission as known in Hydra. However this has to be under- 
stood it is, in any case, a phenomenon quite distinct from the 
kind of fission which shall be mentioned on the following pages. 
The present writer has observed the spontaneous fission at two 
occasions. 
During the months of May and June 1914 I worked at the 
marine laboratory at Plymouth in England, carrying out somé oil 
periments of hatching and rearing medusæ and hydroids in aquar!å 
provided with "plungers" as constructed and described by E. !- 
Browne (1897). At the beginning of May some colonies of 
Laomedea longissima were placed in one of the jars. Very soon 
a number of medusæ were deliberated. Two days later I observed 
— a large number of small hydroid polyps on the plunger-plate and 
