374 ON POLYCERCUS, 



also know from Grassi and RovelU's* account of the development 

 of the Cysticercoid of Taenia elliptica that the development by 

 progressive invagination also obtains. 



In some respects Polycerciis is more nearly related to Staphylo- 

 cystis than to any other known form of Cestode larva. In both 

 the development is a process of external j)'>'oliferation from the 

 product of the hooked embryo — the essential similarity of the two 

 cases being somewhat disguised by the development in Polycercus 

 of an adventitious investment or kyst, not represented in Stapliy- 

 locystis. But Villot'sf account of the mode of formation of 

 the Cysticercoid differs widely from what we have observed in 

 Polycercus. He describes the bud as forming a hollow vesicle or 

 cyst, within which is formed an internal hollow bud, which grows 

 until it comes into apposition with the opposite wall of the cyst, 

 when it becomes invaginated — the wall of the cyst giving rise to 

 the caudal vesicle, the proximal part of the internal bud to the 

 "body" and the invaginated part to the head. 



Summary of Results. 



(1) The hooked embryo in Polycercus develops into a rounded 

 cellular body, which becomes enclosed in a cyst probably entirely 

 of an adventitious character. 



(2) Buds are given off from the periphery of the mass and 

 develop into Cysticercoids, which soon become free in the interior 

 of the cyst. 



(3) The head, with its hooks and suckers, is developed from 

 the central portion of the solid bud ; the middle layers form the 

 'body' and the outermost the caudal vesicle. 



(4) Polycercus is not nearly related to Echinococcus^ but finds 

 its closest ally in Staphylocystis. 



* " Embryologische Forschungen an Cestoden." Centralbl. f. Bakterio- 

 logie u. Parasitenkunde, v. Band (18S9). 



t "Migrations et Metamorphoses des T(^nias des Musaraignes." Ann. 

 Sci. Nat., 6me. serie, Tome viii. (1878). 



