106 
with the chitinous filament, and leads a pelagic life (Plate 
IV., fig. 4. Nat. size 23 mm.). This condition is fre- 
quently found in collections of plankton, and unless care 
be taken may readily be confused with immature stages 
of allied forms. I. C. Thompson, F.L.S.,+ was the first to 
recognise certain copepods taken in collections of plank- 
ton from Liverpool Bay, &c., as the young of Lernea, from 
Claus’ figures. The presence of the males of Lernewa in 
plankton is to some extent accidental, as only the females 
lead a pelagic life. The males remain on the gills after 
the females have gone. The result of the examination 
of the contents of a fine filter, through which the waste 
water was passed from the tanks containing flounders in 
the Piel Hatchery, showed that females were always more 
numerous than males. The ratio, after a number of 
trials, was found to be one male to twenty-five females. 
At the conclusion of the pelagic life the young Lernwa 
again fixes itself to the gills of a fish, and the retrogres- 
sive metamorphosis commences. The parasite buries its 
cephalo-thorax into the tissues. This region then 
develops into horns, which are situated one at each side 
and one dorsal. These pass out at right angles to the 
body into the tissues of the host. At first they are simple, 
but by gradual division in each horn they acquire the 
characters found in the adult (Plate V., fig. 8). The 
anterior part of the segment curves over, taking up the 
position shown on Plate V., fig. 4. The eyes, antennules, 
antenne, mandibles and maxille disappear, leaving only 
the first maxillipedes, which are represented by small 
hooks in the adult. The free thoracic segments fuse, but 
the feet remain as in the cyclops stage. The genital 
segment elongates until fully fifteen times the original 
+ Revised Report on L.M.B.C. Copepoda. Trans. L’pool Biol. Soc., 
vol, vii., p. 212. 
