70 PROF. G. 0. SARS ON THE COPEPODA [Jan. 12, 
understood, that not rarely it may happen that parcels of mud 
adhering to the feet of such birds and containing germs 
of small organisms, may be transported from one basin to 
another for rather a long distance. Several of these germs, for 
instance the resting ova of Rotatoria, Planaria, Bryozoa, and 
small Crustacea, may be kept for years in a dried condition, 
without losing their developing power, and of course will easily 
develop when brought under favourable conditions. Even in 
the case of animals, which do not produce such resting ova, 
a successful transport in this way may be effected. A very 
interesting discovery has recently been made by Prof. Birge and 
Mr. Juday at the Laboratory of the Wisconsin Geol. and Nat. 
Hist. Survey, in the case of a common species of the genus 
Cyclops (C. bieuspidatus Claus)*. It has been stated by these 
authors that this form, at certain periods of the season, is 
subjected to a peculiar encysting process, small, still immature 
specimens enveloping themselves with a rather firm cocoon of 
muddy particles held together by some glutinous matter. It is 
very easy to believe that such cocoons may be kept in a dry 
condition for a long time without any damage to the enclosed 
young Cyclops, and that consequently an accidental transport of 
them by migratory birds may be as successful as that of true 
resting ova. It also appears very probable that a similar en- 
cysting process may be found to be present in other species of 
this genus. In any case, the discovery of Prof. Birge and 
Mr. Juday cannot fail to throw an unexpected light upon 
certain difficult questions regarding the distribution of some 
species of the genus Cyclops, and perhaps also of forms not 
belonging to that genus. 
The above remarks on the accidental transport of animals by 
the aid of migratory birds, chiefly concerns true freshwater forms. 
However, as the said birds not only visit freshwater lakes. but 
also the coasts of the sea, it is evident that a transport of mud 
from the sea-shores to freshwater lakes may occasionally take 
place. In most cases, certainly, the germs contained in such 
mud will not develop when brought into purely fresh water, 
yet it is not impossible that the development of some few forms 
may in reality be effected under such circumstances. This 
may be assumed to be the case with marine animals that have 
accustomed themselves to live in more or less brackish water, 
and this is precisely the case with the type species of both the 
two above-mentioned genera. One of them, /lyophilus flexibilis, 
has even been stated by Prof. Lilljeborg to occur occasionally 
also in purely fresh water, having been found, besides in the 
Baltic, also in the neighbouring Lake Melaren, and this fact 
clearly proves that such brackish water animals in reality possess 
the power of accustoming themselves to living in fresh water. 
It has been stated above, that no less than eight different 
* “ A summer resting-stage in the development of Cyclops bicuspidatus Cls.” 
