366 THE DEVELOPMENT OF CESTODES. 



\vere all simple, round, or pear-shaped bodies, some of very minute 

 size, which seem to pass directly by growth and formation of suckers 

 into the definite larval form. Their origin is uncertain, though Gruber 

 suggests their connection with the hookless Tcenia torulosa of our 

 white fish. This is corroborated by the fact that I once found a 

 number of young Tcenice in the intestine of a loach, which perfectly 

 agreed in size and appearance with the forms described by Gruber, 

 and in addition to the calcareous corpuscles also exhibited four coiled 

 vessels running down the body. 



The demonstration of the nature and history of the ordinary Cysti- 

 cercoid condition does not, therefore, complete our knowledge of the 

 development of the Tcenice, as is further evidenced by the observations 

 made by Mecznikoff in Odessa on a parasitic " Uchinococcus-likQ" 

 larval stage of an otherwise unknown twelve-hooked Tcenia. 1 This 

 Echinococcus-likQ form was found in the body-cavity of the common 

 earth-worm. . In its mature condition it consists of a thin-skinned 

 bladder (Fig. 213, E\ which contains a varying number (up to 

 thirteen) of small Cysticerci of about 0*5 mm. in diameter. 



FIG. 213. Development of an Echinococrus-llke Cysticercoid from the 

 body-cavity of the earth-worm, after Mecznikoff. ( x 25.) 



Although the latter lie quite free in the interior, and possess, 

 like the ordinary Cysticercoids, the distinctive caudal bladder, they 

 are of very unusual origin, inasmuch as, instead of developing directly 

 from the six-hooked embryos, they arise by proliferation of the wall 

 of the surrounding bladder (Fig. 213, B). The bladder is thus the 

 brood-capsule of the enclosed Cysticercoids, and corresponds in some 

 respects to the brood-capsule of the Echinococcus, or perhaps to a 



1 Verhandlungen d. Petersburger Naturf. Versamml., Zool, pp. 263-266, 1868 (in 

 Russian). The worms were given to ducks, but without result. According to the 

 structure of their hooks they close resemble, if they be not identical with, Tcenia nilotica, 

 Krabbe, from the intestine of Cursor isabcttinus. 



