76 21iscellaneous. 



of the caudal vesicle 0*0G. From these measuremeuts one may judge 

 of the minuteness of our parasite, and the difficulties presented by its 

 study. Its bulk does not exceed that of an lufusorian ; and it is 

 evident that it would escape the researches of any observer who 

 does not avail himself of the lens and the microscope. 



As indicated by its name, Urocystis proJifera\s> essentially charac- 

 terized by its mode of multiplication. Its buds are successively 

 developed, and become detached as soon as they have arrived at 

 maturity. Thus its colonies are usually composed only of two indi- 

 viduals placed one behind the other — a completely-developed vesicle 

 in front, and a bud in the form of a caudal appendage. The bud is 

 represented at first only by a small spherical vesicle containing 

 cellular elements in course of proliferation. It is sessile, and in 

 continuity of tissue by its anterior extremity with the individual 

 that preceded it (perfect vesicle or bud) ; but during development 

 it acquires an oval form, and tends gradually to become isolated. 

 At the moment when the first traces of the scolex make their ap- 

 pearance the two individuals are no longer united to each other 

 except by a thin cord. When it becomes detached, the vesicular 

 bud has acquired its full development, and contains a perfectly- 

 formed scolex. The latter speedily frees itself from its caudal 

 vesicle to go and encyst itself in the adipose bodj' of its host ; but 

 the scolex, while abandoning its caudal vesicle, remains encysted in 

 its, receptaculum capitis and does not evaginate its trunk. The 

 escape of the scolex may be effected either by degenerescence of the 

 caudal vesicle or by rupture of the pedicle which attaches the scolex 

 to the vesicle. The latter mode, which I have frequently observed, 

 appears to me the more natural. 



The scolex, in becoming encysted in the adipose body of its host, 

 does not undergo any great modification. There is nothing more 

 than a change of external form and a thickening of the integuments. 

 It becomes spherical ; and the embryonic elements which constitute 

 the wall of the receptaculum capitis pass to the state of elastic fibres, 

 to replace the caudal vesicle as a protective organ. 



No doubt, independently of its habitat, Urocystis prolifera has 

 many relations to Stapliylocystis ; but it differs from the latter 

 by important characters which fully justify the establishment of a 

 genus. In Staphylocystis the individuals which constitute the colony- 

 are developed simultaneously, and do not separate from each other 

 at maturity. The scolex does not issue from the caudal vesicle, 

 and has not its trunk invaginatcd upon itself. 



The other states of this new form of worm are unknown to me, 

 and probably have not yet been described ; but we know now that 

 the scolex which must figure at the head of the strobile possesses a 

 long trunk and a simple circlet of very small hooks. Aa to the 

 definitive host, whether mammal or bird, it certainly belongs to 

 the Alpine fauna. The Glomeris which furnished me with Urocystis 

 prolifera was captured in the woods of the Grande-Chartreuse. — 

 Comptes Rendus, December 6, 1880, p. 938. 



