160 SIR W. A. HERDMAN : RESULTS OF CONTINUOUS 
into consideration, the poorest years in the series are 1913, ’14, and 716, 
and the most favourable for Lamellibranch larvæ 1918 and 719. 
Gastropod larvæ are never present in our gatherings in such quantity as 
the Lamellibranchs, and their general distribution throughout the year 
is much the same. 
OCEANIC AND NERITIC SPECIES. 
During certain of the years (especially 1909 and '10) we made a careful 
analysis of the species which are commonly supposed to be of “ oceanic ” and 
“ neritic” origin, with the view of ascertaining to what extent outside 
influence affected the plankton of the Irish Sea. Oceanic species* are those 
“holoplanktonie” forms which typically inhabit the open ocean, although 
they may also be found in coastal waters, a; d which have no fixed or resting 
bottom stages in their life-history. Neritic species are those typically found 
in coastal and comparatively shallow waters. Most of them have fixed or 
resting bottom stages in their life-history, and so belong to the meroplankton, 
but some neritic forms are holoplanktonie, being permanently free. 
In our third Annual Reportf, there is a full discussion of the occurrence 
during the three preceding years of the oceanic and neritic species, leading to 
the general conclusion that the organisms of the Port Erin plankton are on 
the whole chiefly neritic, the percentage of oceanic forms ranging during the 
three years from 30 to 60 per cent. If the numbers of neritic occurrences 
be added up for each month, they show that mid-winter (December and 
January) and mid-summer (July) are more oceanic in character than the 
intervening months, and that April, May, and October are the most neritic. 
The oceanic forms, although not always the most abundant, constitute the more 
permanent element of the plankton, the meroplanktonic neritic forms showing 
periodic increases and reductions in accordance with the life-cycles of the 
organisms concerned. 
REPRESENTATIVE NATURE OF PLANKTON HAULS AND 
SAMPLES. 
In regard to the comparative value, or catching power, of different nets, 
our experiments showed that as a deep-water net for vertical hauls the 
“Nansen” was much more convenient, reliable, and effective for work at 
sea, and especially in rough weather, than the ** Hensen.” 
The ** Shear-net” (the Heligoland “Sherbrutnetz”), with one square metre 
* There are, however, some holoplanktonie forms (such as Sagitta) which seem to be 
equally at home in the open ocean and the coastal waters all the year round, and which 
may be called “ panthalassic." Their presence along with neritic species cannot be taken to 
indicate any inflow of oceanic water. 
t Trans. Biol. Soc. L'pool, vol. xxiv. 1910, p. 245. 
