Compatibility in Trematodes and Molluscs — Cheng 
149 
Fig. 3. Photomicrograph showing Fasciola gigantica miracidium which has 
shed its epidermal plates after exposure to a 1:10 dilution of Galba ollula 
plasma; 1 minute after exposure, se, Shed epidermal plates. 
Fig. 4. Phase-contrast photomicrograph showing invagination of apical 
papilla of Fasciola gigantica miracidium and secretion of lytic enzyme ( ?) after 
exposure to concentrated Galba ollula plasma, ip, Invaginated papilla; s, secreted 
material. 
multiplication of the cells of the mother sporo- 
cyst wall which invaginates and surrounds each 
daughter sporocyst. More recently Schell (1961, 
1962^), who studied the sporocysts of Hap- 
lometrana intestinalis and Glypthelmins qua eta, 
has expressed the opinion that the paletot is not 
of parasite origin but represents an enveloping 
membrane which has resulted from the prolif- 
eration of the basement membrane surrounding 
the snail’s gut, thus preventing further invasion 
by the mother sporocyst beyond that space de- 
limited by the intestinal epithelium on one side 
and the basement membrane on the other. If 
Schell’s observations are correct, the reason why 
mother sporocysts of H. intestinalis and G. 
quieta are found abutting upon their molluscan 
