ANATOMY OF LIMNOCNIDA TANGANYICA. 285 
its life-history before any attempt is made to fix its abode 
definitely. 
The only fact we have at present about the life-history of 
the Medusa is that during part of April, May, and June, 
swarms of male, female, and asexual bud-bearing individuals 
coexist in Lake Tanganyika. The most important problem 
to be solved is, Does Limnocnida pass through a fixed 
hydroid stage in any part of its life-history? Is its develop- 
ment metagenetic or hypogenetic ? 
It is certainly possible that, as in the case of the Narco- 
medusz, there is no fixed hydroid stage. It seems to me 
conceivable that a kind of alternation of generations may occur 
in Limnocnida such as has been described by Brooks (8) in 
Willia ornata (ifrightly identified), in which asexual Medusze 
produce sexual forms by budding. It is possible that the sexual 
individuals of Limuocnida may produce eggs which develop 
into free-swimming planula-larve which grow into the asexual 
Medusz, which in their turn give rise to sexual Meduse by 
budding. 
On the other hand, if a fixed hydroid stage form part of the 
ontogeny, Limnocnida must be separated from the Narco- 
medusz which do not pass through such a stage, and then 
would have to be regarded as descended from an Antho- 
medusa-like ancestor and as having developed sense-organs 
with an endodermal axis, just as Limnocodium is to be 
regarded as a descendant of the Leptomedusz with sense- 
organs morphologically similar to those of the Tracho- 
meduse. 
With regard to the striking similarity of the sense-organs in 
both the fresh-water Meduse, Limnocodium and Lim- 
nocnida, I can only consider it to be another instance of 
parallel but independent evolution of similar organs in two 
genera which are not related to one another, but which live 
under similar conditions (“‘ homoplasy ” of Lankester, cited by 
Darwin, ‘ Origin of Species,’ 6th edit., p. 385). If this is 
really the case, the similarity of structure is most remarkable. 
