114 GEORGE LEFEVRE AND WINTERTON C. CURTIS 
section, while a few loose epithelial cells are sloughing off at the 
edges of the growing cyst — a not infrequent occurrence during 
the early stages of implantation. Fig. 36 shows the completion 
of the process, and the glochidium is now, after three hours in 
this case, entirely enclosed within its epithelial covering. 
LIBERATION FROM THE CYST AND POST-LARVAL STAGES 
In about one week as a rule after attachment, the wall of the 
cyst begins to assume a looser texture, the intercellular space 
becoming infiltrated with lymph, and from this time on to the 
end of the parasitic period there is little further change in its 
structure. 
Before liberation of the young mu'ssel, the valves open from time 
to time and the foot is extended. By the movements of the latter 
the cyst is eventually ruptured, its walls gradually slough away, 
and the mussel thus freed falls to the bottom. Fig. 33 shows an 
early stage in the breaking up of the cyst which is seen to be com- 
ing off in patches on one side. Portions of the wall of the cyst 
often adhere to the shell after liberation, while, if the young mus- 
sel has hooks, it may hang for a time by shreds of the fin in which 
the hooks are embedded, as seen in fig. 12. 
We have not succeeded in keeping the young mussel alive in 
the laboratory for a longer period than six weeks. From the first 
they are very active and creep about in a dish by stretching out 
the foot, securing a hold by flattening the distal end against the 
bottom, and then drawing up the body after the fashion of other 
small lamellibranches. Fig. 29 gives an excellent illustration of 
the various positions assumed as they crawl about, and also shows 
the extent to which the shell has developed beyond the margins 
of the glochidial valves by the end of the first week of free life. 
