124 



supplies the heads with the substance necessary for their develop- 

 ment through those fine cords. For the rest, I will not undertake 

 to decide whether all those larger and smaller vesicles, which con- 

 tain EchiHococcus-hea.ds and float about free among fully-developed 

 Echi7iococciis-heads in the cavity of the parent vesicle, are de- 

 tached from the wall of the latter, or whether some few of them 

 do not arise from the free Uchmococcus-heads themselves, which 

 have developed JEchinococcus-germs in their interior, and afterwards 

 become distended into vesicles by them ; I was often surprised, in 

 fact, to find upon free vesicles containing Echinococcus-heads, hooks 

 attached, perhaps remnants of the destroyed circlet of hooks. In 

 such vesicles of E. variabilis, in fact, I believe I could trace re- 

 mains of the suckers. "With greater difficulty can we understand 

 the mode of origin and propagation of the maternal vesicle of the 

 Echinococci. Since in Echinococcus hominis we often find smaller 

 hydatids enclosed within larger ones, we must believe that the ex- 

 ternal hydatid is the parent in which the others have been sub- 

 sequently produced. In what manner, however, this enclosure has 

 taken place, I must leave as much unsolved as the origin of the 

 parent vesicle itself." 



The next step wa» made by Dr. Lebert, in his excellent paper 

 (unfortunately without figures), " Einige Bemerkungen iiber Blasen- 

 wiirmer," in Miiller's Archiv for 1843. From this I make the fol- 

 lowing extracts : — 



" In the most, even freshly examined hydatids, the animals no 

 longer move. Yet not unfrequently, if many vesicles be examined, 

 living groups may be met with. The movement of the animal, while 

 still in the maternal vesicle, consists partly in turning upon its axis, 

 partly in a wavy contraction, comparable to a peristaltic movement. 

 In the interior of these yet living and moving animals I have per- 

 ceived ciliary motion very clearly. It appeared in the whole interior 

 of the animal, and I could observe it for hours together. At first I 

 could with difficulty distingviish the single vibrating cilia ; yet, partly 

 after partial evaporation of the fluid in which the animals were con- 

 tained, partly by modifying the light with a very fine perpendicular 

 diaphragm, I could succeed in seeing the cilia themselves, which are 

 slightly curved aud somewhat hook-like, and hardly more than 

 -g^mm. in breadth. I have seen the single cilia with especial 

 distinctness towards the margin of the animal ; commonly, however, 

 they are indistinct, on account of the contemporaneous %dbration of 

 a certain number of cilia, which resemble in their motion a field of 

 corn agitated by the wind. The observation of this ciliary motion 

 was perhaps rendered more easy by the circumstance, that I observed 

 the animals still adherent to the finely granular membrane which 

 forms the parent vesicle, and which, in all probabiUty, favourably 

 modified the light." 



" As to what concerns the development of the vesicles themselves, 

 it seems to go on in the following manner : — upon the inner wall of 

 a cyst which contains Echinococcus-cysts, secondary cysts are formed, 

 which, after they have attained a certain grade of development, be- 



