19 
inside the pupal antennæ is distinctly seen a longer and more sickle- 
shaped claw, quite resembling that of the adult parasite; in the 
antennules and their setæ the corresponding structures are visible in 
a more developed form; and in the abdominal feet are very con- 
spicuous distinctly segmented swimming-feet, in every detail agreeing 
with those of the adult; the long and elegant setæ with their deli- 
cate plumules are ensheathed in the shorter and bigger ones of the 
pupa (cfr. Fig. 24), and in the furcal setæ of the latter the longer 
ones of the next form show plumules. Any genital openings I have 
not been able to observe. 
In casting off the pupal cuticle this enclosed 
Copepod probably gives up the fixed condition. 
As young males and females they leave the 
empty pupal shells on their former host, swim 
away and live for a while in a free state, in 
whicli they copulate. After copulation the 
males probably die, while the impregnated 
females again seek the same species of fish 
and take up the parasitic life anew, but in 
a more intense form: they pierce the skin of 
the fish and, gradually growing, penetrate 
through the muscles and reach by and by to 
the intestines of their host. The course of events here set forth, 
I am sorry to say, is not founded on direct observation; but any 
reader remembering the facts known from Lernæa branchialis will 
certainly find the above conjecture fairly plausible. 
Directly observed are some early stages of the boring parasite, 
the structure of which does not deviate very much from that of 
the Copepod, seen enclosed in the pupa E. As before mentioned 
they appear externally like small, pale cones of 0,5—2 mm. length, 
protruding through the skin of Scop. glacialis. I have dissected 
out 3 specimens. The one has a total length of 6 mm.; it pro- 
jected as a 2 mm. long, siender thread from the back, just in front 
of the dorsal fin, of a fish of 57 mm. length; it was only inserted 
2 * 
Fig. 4. Last pupal 
stage (E). Termiual 
part of setæ of foot, 
showing extremely 
delicate plumules. 
