217 
plate was 75 of that of the jar, and one movement 35 cm up- 
wards and as much downwards occupied 2 minutes. It was a move¬ 
ment much more gentie than the ripple for which the colonies are 
exposed when growing on a bulwark or a breackwater, and no 
traces of frustules were observed in colonies preserved directly 
after coming on shore. — It is a matter of faet, that the colonies 
were starving, as I did not know how to find suitable food for 
them, and it seems to me to be very probable that the fission 
was the result of the starvation. 
During the year 1915 I have examined a very large material 
of Laomedea geniciilata collected at different seasons in Middelfart 
Sound (Lille Belt), where as a rule there is a very heavy current and 
frequently a considerable ripple at the bulwarks on which a great 
part of the material was collected, and not a single case of fission 
has been observed in this material. — On the other hånd, the 
frustules of L. geniciilata described above were found on colonies 
collected on the inner side of the pier at Frederikshavn, where 
the water is comparatively quiet. Various facts indicate, that these 
colonies lived under unfavourable conditions. The faune in the 
waters at and round Frederikshavn was remarkably poor at the 
time in question, when compared with what I have seen at pre- 
vious times. Laomedea geniciilata was rare everywhere, except in 
deeper water, where I dredged some badly looking colonies growing 
on Halidrgs. Tiihularia and Clava, which use to be common on 
the stone reefs, were totally absent, and Mgiiliis was absent inside 
the piers and rare outside. 
The development of a hydranth with its many tentacles demands 
a larger amount of energy than the continual growth of a simple 
thread. This circumstance seems to me to make it reasonable, that 
starvation may cause some of the buds on a colony to continue 
their growth and become thread-like in stead of developing into 
hydranths. 
The abllity of reproduction by spontaneous fission is undoubt- 
edly a factor of importance for the species in which it oceurs, 
as under unfavourable conditions (lack of food?) they are able to 
develope and deliberate, within a short Space of time, a consider¬ 
able number of frustules with the possibility of being carried away 
to more favourable localities. 
