LIFE-CYOLK OF " CYSTOBIA " IRRFGllLARTS (mINCII.). 27 



is only necessary to compare my figs. 5, 29, etc., showing a 

 genuine peritoneal investment enclosing C. irregularis, to 

 see the difference. The peritoneal sac by which young 

 Diplocyst is-couples appear to be first attached to the gut- 

 wall (see Kunstler's figs. 18 and 19) undoubtedly breaks and 

 liberates the parasites into the coelome. 



The investing membrane. — The investing membrane 

 is homogeneous and, for the most part, fairly thin but firm 

 and tough. Around the greater part of the body it closely 

 surrounds the next internal layer, which is a delicate limiting 

 membrane {l.m.), quite comparable to that of Cystobia. 

 About the plane of junction, however, where the regular 

 contour is broken by the V-shaped groove, the investing 

 membrane or ectocyst leaves the body proper, as is shown 

 in the figures. Its middle poi'tion just here is invariably 

 thickened and usually of a triangular shape. Between the 

 ectocyst and the limiting membrane there is a space (sj).) of 

 varying size. This I regard as being due to the contraction 

 of the investing membrane. In the fresh condition the 

 thickened ectocyst probably fills up this space and is in con- 

 tact with the limiting membrane, and this part is represented 

 in the section by the triangular tongue (t), the shrinkage 

 having been doubtless caused by fixation. 



In other words, the investing membrane in D. schneideri 

 is evidently secreted at all points where the limiting-mem- 

 brane and ectoplasm remain free after association of the 

 parasites. This thickening of the ectocyst in the plane of 

 junction must considerably strengthen the union of the 

 couple, just at the point where it is most required, and thus 

 minimise the risk of dissociation. So there is a slight dis- 

 tinction between the formation of the ectocyst here and that 

 of the membranes surrounding an ordinary syzygy when it 

 becomes encysted. While, in the latter case, the ectocyst is 

 only secreted by tlie posterior ends of the Gregarines and 

 forms an approximately spherical cyst (owing to the rotation 

 of the animals), here it is secreted at all points of the body 

 equally, and is laid down in the form of the couple. It 



