Zoological Society, 393 



lar to that which Prof. Midler has already so beautifully described 

 in the development of a peculiar kind of hydatid tumours. 



In his Article "Parasiten" (Wagner's Handworterbuch d. Phy- 

 siologie, bd. 2, 1844), Von Siebold, after recapitulating his view of 

 the development of the Echinococci contained in Burdach's Physio- 

 logie, makes the following highly suggestive remarks : — 



" Clearly as we can trace the development of the young of the 

 Echinococcus, we understand very little of the mode in which the 

 pill-box (eingeschachlelt) aggregations are produced. The multipli- 

 cation of the vesicles certainly does not take place by division, nor by 

 the formation of buds upon the outer surface of the parent cyst, as 

 some have supposed. The hypothesis remains, that the young Echi- 

 nococci cast off their circlet of hooks, become distended, lose their 

 suckers, and so change into little Echi?iococcus-vesic\es, in which 

 a new brood then becomes developed. I must indeed confess that I 

 have not directly observed this process. In any case, the young 

 Echinococcus must be in a fit state to wander ; and if it should be 

 made out that new Echinococcus-vesic\es proceed from them in the 

 interior of the parent vesicles, we might also justly assume that the 

 young Echinococci, wandering into other organs, or even into other 

 persons, may thus lay the foundation for new colonies. Whether, 

 again, there exists a special cestoid worm provided with sexual organs, 

 with which the Echinococcus- vesicles stand in the same relation as 

 the Cercaria-sa.cs do with certain Trematoda, time will show. If it 

 be so, the young Echinococci must change, having become separated 

 from their pedicle, not into Echinococcus-vesicles, but by the elonga- 

 tion of the body into Tcenice." 



Finally, in the ' Verhandlungen der Physikalisch-Medicinischen 

 Gesellschaft zu Wurzburg' for 1850, (to which my attention was 

 drawn by my friend Mr. Busk,) I find the following notice : — 

 "Herr Virchow described the ciliary movement which he had observed 

 in the stem by which the young Echinococci hominis of Man are 

 attached to the maternal vesicle, — a new observation for this genus." 



I have here endeavoured to notice all those Memoirs which, at the 

 time of their publication, made a definite addition to what was already 

 known upon the structure of Echinococcus. The literature of the 

 subject is somewhat voluminous, and hence the necessity of this 

 limitation, and the consequent absence of any account of the valuable 

 memoirs of Goodsir, Curling, Busk, and Erasmus Wilson, all of whom 

 had been anticipated by the continental observers. 



EXPLANATION OF PLATE XI. 



Diagrams : — Hypothetical representations of — A. a young Tamia; B. a Ccenurus; 

 C. a Cysticercus ; D. the same, encysted; E. a Cysticercus, encysted, 

 enlarged, and developing many heads (like Coenurus) from the upper 

 portion of its outer (now inner) surface; F. a similar form, which de- 

 velopes heads from the lower portion of its outer (now wholly outer) 

 surface, and so becomes an Echinococcus cyst. 



