32 MR. F. J. MEGGITT ON A 
backs infected by this parasite be kept in an aquarium, it is no 
uncommon sight to see them with °5'—-2" of cestode hanging out 
of the anus. The proglottides first emptied degenerate, and all 
traces of segmentation become obliterated, until by the time the 
last eggs are discharged, the distal end has become an unrecog- 
nisable shapeless mass. The whole cestode is then discharged 
with the feces, and this is often followed by the death of the 
fish. 
Some time after entering the water, the onchosphere escapes 
through the hole in the second membrane to lie freely inside the 
outer one. Since the diameter of the hole is less than that of the 
onchosphere, the latter is considerably contracted in its passage : 
the third membrane is often dragged out with it, but it may 
he ruptured and left behind, The cause of this escape may be 
possibly due to osmosis, but it is more probable that it is due to 
the onchospheric movements about to be described. The poste- 
rior portion of the onchosphere is always under the aperture 
in the second coat, so that the movements would have a ramming 
effect upon the delicate third membrane, and either rupture it or 
drag it out. The pressure of the coverslip is not the cause, for I 
have often seen similar movements in onchospheres lying freely 
in a watch-glass. . Yolk-follicles are often scattered within the 
membrane at the time of the escape. 
The onchosphere now exhibits curious movements (I have only 
seen them in the free onchosphere, but it is fsrobable that they 
occur also before the escape takes place). It slowly contracts 
Text-figure 5, 
Drawing to show movements of onchosphere. 
antero-posteriorly, stretching out its hooks as far as possible; the 
extreme anterior point often forms a small depression surrounded 
by avidge. With a quick jerk it elongates itself along the same 
line, at the same time striking downwards with its hooks until 
they lie flat against the body. It then contracts as before. The 
movements are repeated indefinitely, and are probably for the 
ultimate purpose of attaching the onchosphere to the alimentary 
canal of its host. 
La Rue (11) reports similar movements in the onchospheres of 
