HYDROID PHASE OF LIMNOCODIUM SOWERBYI. 511 
three or four species of Cunina, Metschnikoff found that im- 
mature sexual cells separated themselves from the generative 
organs, both in males and females, and proceeded to multiply ; 
that one of these cells became engulfed by another, and, thus 
protected, divided and re-divided to form a morula, which under 
certain circumstances developed into a medusa. Such a “male 
parthenogenesis” may occur in Limnocodium, and would 
account for several facts otherwise inexplicable. 
The evidence on the matter is unfortunately but slight. 
Against the view of Brooks may be urged (a) that the hydroids, 
which have practically no power of locomotion, are to be found 
in the greatest numbers on the submerged sagittate leaves of 
various Nymphee in the tank, which die down every year, a 
fact which seems rather to imply a free-swimming larva, and 
which is therefore somewhat in favour of one of the other 
hypotheses; (b) that the hydroid spreads into other tanks 
which are in connection with the water system of this one,}! 
which seems to point in the same direction; (c) that the 
Victoria Regia tank is drained almost every winter, and lies 
nearly dry for a period varying from one to three months, 
which suggests that an ovum or gemmule with a cyst capable 
of resisting violent changes in the environment is necessary for 
the continuance of the species, the ordinary coating of the 
hydroid being obviously inadequate for the purpose. In favour 
of the third possibility is Bourne’s statement that the genital 
sacs of the adult medusoids, after liberation of ripe spermatozoa, 
become nipped off, fall to the bottom, and live for some time 
at least without disintegration. 
On the question of the systematic position of Limnocodium 
the foregoing observations do not throw much light. While 
Lankester assigned it to the Trachymeduse, Allman and 
others regard it rather as belonging to the Leptomeduse. On 
the one hand, no Trachymedusan has been observed to pass 
through a hydroid phase; on the other, the structure of the 
1 That no meduse have been seen to live in these tanks is probably due to 
their lower temperature, 
