Zoological Society. 391 



generally elongated, to those which we have found in the neck of 

 Ccenurus. In the fluid which the maternal vesicle encloses, we meet 

 with a few Echinococci, which when they have everted their coronet 

 of hooks and their suckers, allow nothing to be perceived in their in- 

 terior but a few scattered glassy corpuscles. These Echinococci evi- 

 dently arise from the inner surface of the parent vesicle. My own 

 observations hereupon have been made upon E. hominis, E. veteri- 

 norum, and a new species which, since the number of its suckers 

 varies very much, I will call E. variabilis. On examining the inner 

 surface of the parent vesicle we see little vesicles attached here and 

 there, which contain a finely granular substance ; out of this mass 

 the Echinococci proceed (hervorkeimen), sometimes oxdy one, some- 

 times two, six, seven or more. A portion of the granular mass be- 

 comes, in fact, sharply marked off, forms a small roundish body, 

 which, however, by one of its ends, still clearly passes into the rest 

 of the substance ; the rounded body gradually takes on a pea shape, 

 the constricted portion elongates, and the body, which has now 

 assumed a more oval form, is connected only by a delicate viscid 

 thread with the mass from which it sprang ; we soon now observe in 

 the interior of the body the circlet of hooks and the glassy corpuscles. 

 The Echinococcus-he&d thus far developed now begins to move — 

 everting and retracting its suckers and hooks ; the whole body being 

 at the same time sometimes elongated, sometimes contracted. The 

 development of the Echinococci having proceeded to this stage, the 

 delicate membrane in which they are enclosed bursts. The young 

 Echinococci do not immediately fall out, for they are all connected 

 to the inner surface of the membrane, which until now has enclosed 

 them, by means of a delicate cord or process of the latter, which 

 penetrates at the posterior extremity of the Echinococcus, through a 

 pit, into the interior of the body of the Echinococcus. The pit looks 

 almost like a sphincter, holding just that cord of the membrane ; 

 only after an interval do the cords and the bodies of the Echinococci 

 become separated. The mode of connection of these cords with the 

 bodies of the Echinococci, and their separation from them, reminds 

 one completely of the relation which the bodies and tails of the Cer- 

 cariee have to one another. The membranous covering of the young 

 Echinococci wrinkles up immediately when it is torn. The Echiuu- 

 cocci become everted, and so form a rounded heap, in the middle of 

 which the collapsed investment lies hidden, the Echinococci being 

 attached to it like the polypes upon a polypidom. 



" Such masses of Echinococci either remain for a long time hang- 

 ing to the inner surface of the parent vesicle, or they become de- 

 tached from it before the single Echinococci have separated from the 

 wrinkled membrane. The granular mass contained in the vesicles is 

 probably comparable with nothing else than with a yelk mass, which 

 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 Echinococcus-ke&ds and float about free among fully-developed 

 Echinococct(s-\iea.ds iu the cavity of the parent vesicle, are de- 



