370 ON POLYCEKCUS, 



to, as well as upon the observations of Yillot. The tigures 

 represent a form of Cysticercoid different from that now under 

 consideration, and the account given of the development is not 

 readily reconcilable with what we have found in the parasite of 

 D id ymog aster. We will quote here Leuckart's account in full: — 



*' In its mature condition it consists of a thin-skined bladder, 

 which contains a varying number (up to thirteen) of small Cysti- 

 cerci of about 0"5 mm. in diameter." 



" Although the latter lie quite free in the interior and possess^ 

 like the ordinary Cysticercoids, the distinctive caudal bladder, 

 tley 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. The bladder is thus tlie 

 brood-capsule of the enclosed Cysticercoids and corresponds in 

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

 to a Cce/iwrifs-bladder, and, like these, is undoubtedly to be referred 

 to the six-hooked embryo. The first developmental stage observed 

 bv Mecznikoff appeared to be a solid ball of about O'OS mm., with 

 an unusually thick cuticular envelope and cellular contents. The 

 Litter subsequently became clear on attaining a diameter of 

 OH mm., when the embryo lies on the inner surface in the furm 

 of a cellular layer. Soon the buds begin to form, and that exclu- 

 sively from the cellular wall, which becomes thicker at certain 

 spots and sends little projections into the inner cavity. Although 

 at first flat and connected by their broad bases with the cellular 

 wall, the protuberances, as they grow larger, gradually detach 

 themselves from the subjacent layer. This separation is facili- 

 tated by the development of a hollow space in the interior of the 

 basal portion, so that after a time the bud is only connected with 

 the mother-bladder by a thin filament. Finally this connection 

 is destroyed, and the bud thus becomes an oval body lying freely 

 in the interior. It then proceeds to undergo its further develop- 

 ment. This is essentially the same as that which we have already 

 (ob-)served in the buds situated inside the brood-capsule in the 

 Echinococci, only that in this case not only head and neck are 

 formed, but a third joint, consisting of a kind of caudal bladder. 



