DISTOMUM CIRElGERUM. 281 



thelium (Fig. II, ex. bl.). On the basement membrane, 

 between tlie large isolated cells, there can often be seen 

 nuclei which regenerate fresh giant-cells when required 

 (Fig. X, 01.). The right and left excretory ducts seldom, if 

 ever, open directly into the cavity of the bladder, but 

 they pass into the substance of one of the large cells 

 (Fig. IX, m. d., and X, 2). In this respect the ducts are 

 comparable to the nephridia of certain Chajtopods, where 

 the external opening is closed by a patch of cells, and 

 the excretory matter is passed out through the body of 

 the cells. The bladder opens to the exterior by a narrow 

 and somewhat tortuous channel, which is lined by a thick 

 cuticle continuous with that covering the body. Around this 

 channel there is clustered a group of elongated glandular 

 cells, Avhich apparently pour some secretion into the exit- 

 duct of the bladder (Fig. II, gl. c). 



In specimens preserved in Flemming's solution the large 

 cells lining the bladder contained a variable number of black 

 globules, which disappeared in twenty-four hours if the 

 sections were mounted in xylol balsam, but they were per- 

 manent in chloroform balsam. Flemming ^ has observed a 

 similar disappearance of fat, blackened by his solution, both 

 by means of turpentine and xylol. We may conclude that 

 the black globules consisted of a fatty substance, which was 

 presumably w^aste excretory matter. 



Correlated with the relative paucity of excretory tubules 

 and flame-cells it is extremely probable that the epithelium 

 of the bladder can itself directly absorb Avaste matter from 

 the surrounding parenchyma, for it is scarcely possible that 

 the minute main ducts opening into the substance of a couple 

 of cells could convey into the whole epithelium the large 

 quantity of waste products which it undoubtedly contains. 

 The relative thinness of the muscular coat would render easy 

 such a direct absorption of nitrogenous waste. 



The Encysted Animal. — It was mentioned above that 

 the trematode commonly lives encysted in the muscles of the 

 » Flemming, ' Zeit. f. wiss. Mil;.,' 18S9, p. 39. 



