600 DEVELOPMENT OF THE ECHINOCOCCUS-BLADDER. 



On closer observation, it was also seen that the surface of the 

 Uchinococcus-l)\a,ddeT was not smooth, but broken by numerous fine 

 rents and cracks, which crossed each other and ran in different 

 directions. The same phenomenon was afterwards observed in other 

 Echinococci. It is as though the external layers, which are also the 

 oldest, no longer being able to resist the increasing pressure of the 

 growing mass, had ruptured. It is at least certain that the external 

 cuticular layers are much more tightly strained than the inner ones. 

 It is only necessary to cut the bladder at any point to get ocular 

 demonstration of this fact by the immediate rolling up of the 

 bladder-wall. 



In bladders of about 1 cm. in diameter, on which our description 

 is based, the general thickness of the cuticle was about 0'2 mm. On 

 the internal surface the cuticle is more distinctly defined than on the 

 external, and is laminated throughout its whole thickness. As has 

 already been indicated, this lamination is obviously only the ex- 

 pression of a deposition in successive layers. While the external 

 layers are gradually destroyed, new ones are continually being formed 

 deep down, where the cuticle lies upon the parenchyma of the worm. 

 These are seen chiefly in the form of a distinctly marked border, 

 which extends along the boundary between the parenchyma and the 

 cuticle, and sometimes even remains visible when the former of these 

 is destroyed. The single layers of the cuticle are not, however, 

 always marked off from each other with equal distinctness, nor always 

 of the same thickness. As in the worms under consideration, the 

 latter may be estimated on an average at about 0*0035 mm. 



The parenchyma which extends under the cuticle is, in spite of 

 its significance in the general life of the worm, of slight strength. It 

 hardly ever measures more than 0*12 mm., and on a side view in 

 fresh specimens is distinctly seen to be composed of two layers an 

 outer and an inner, as has already been mentioned in regard to the 

 larger Echinococci from the second experiment. 



The vesicular structures directed towards the internal cavity ap- 

 peared, as in the Cysticerti, as rather sharply defined clear drops, 

 with a somewhat fatty lustre, and not at all unlike the so-called 

 " sarcode-drops." Most of them measured between 0*026 mm. and 

 0*036 mm., but there were some which were twice, or even three 

 times larger. In the external layer the elements had much more 

 emphatically the usual cellular character, although they were also 

 pale, and not very distinctly defined. Their size was markedly 

 smaller, being usually only about 0*07 mm., with the exception of the 

 granular cells, which measured about twice as much. Between the 

 cells there are found numerous coarse, strongly refracting grains, like 



