56 LIVERPOOL BIOLOGICAL SOCIETY. 
By means of a continued series of observations through- 
out the seasons of the year, such as a biological station 
affords, we are enabled to study the distribution not only 
of the various groups but also of the different species. In 
the case of the Copepoda, the facts as regards the species 
are striking though difficult of explanation. A particular 
species may be comparatively abundant at one time and 
then appear to become extinct in the same locality. 
Instances of this occur in the case of Pontella wollastona 
and of Euterpe gracilis, two rare forms alluded to in the 
last report as having been found off Puffin Island, and 
for a time both frequently met with. For many months 
past, however, neither species has occurred in the 
gatherings, though carefully looked for in the same 
localities as heretofore. 
A very striking example of the seeming propensity 
of these minute Crustaceans to congregate in shoals was 
noticed during the ‘‘Hyzna”’ expedition of May, 1888. 
During the whole of the second day, whilst cruising near 
the east and south coasts of the Isle of Man, viz. from 
Douglas to Port Erin, the surface of the water literally 
swarmed with the large and beautiful Copepod, Anoma- 
locera patersonti. Hach cast of the tow-net brought up 
thousands of them; they were so numerous as to be 
distinctly visible to the eye on the smooth edge of the 
waves, and had the appearance of fine dust as seen from 
the side of the vessel. They were equally abundant during 
the day and after sundown, but, strange to say, none were 
to be found next morning, although we were traversing 
the same route as that on which they were in such 
profusion the previous day. Nor have we taken a single 
specimen of Anomalocera since that date, nor for three 
years previous to it, when a single pair was taken in the 
epen sea, near the North-west Lightship. 
