130 TRANSACTIONS LIVERPOOL BiOLOGICAL SOCIETY. 



broken down). There is not the slightest possibility that 

 an A cyst could ever become a B cyst, or vice versa. And 

 now to describe the latter. 



Fig. 6 is part of a section through the periphery of 

 the lower cyst in the appendage of fig. 4. All around 

 (though the upper cyst happens to be close to it on one 

 side) is the infiltration, a condition easier to describe ver- 

 bally than to draw, as it would be most difficult to 

 reproduce except very diagrammatically. 



These pseudocysts arise as the result of an endeavour 

 on the part of the host to limit the infiltrated area by the 

 arrangement of the hypertrophied connective-tissue in a 

 series of concentric layers round the centre of infection. 

 (The marked hypertrophy here is in strong contrast to 

 its complete absence in the A cysts). This re-action of 

 the host, not always so well-defined, seems to be without 

 much success, for the parasitic invasion usually spreads 

 further, often leading to another attempt at restriction ; 

 in fig. 4 for example, the' upper pseudocyst is of later 

 formation than the lower. Young ones, therefore, are 

 simply areas of diffuse infiltration with the layers con- 

 centrically arranged; but, with age, and probably, to a 

 certain extent, the pressure of the surrounding parts on 

 the enclosed tissue, the cells of this latter disintegrate 

 and degenerate, leaving a mass of spores embedded in their 

 remains as a ground-substance, with frequently patches or 

 islands free from spores and staining only with the plasma 

 stain (deg.). The spores are in a much more closely 

 packed condition than in the comparatively loose, infil- 

 trated tissue of the appendage (not shewn in the fig.). It 

 need hardly be added that there is no trace of endoplasm, 

 nor of sporoblast-formation round the margin, nor, of 

 course aii}^ ectorind, and, in fact, no sharply-marked ex- 

 ternal limit — a great contrast to fig. 5. The periphery 



