258 ENTOZOA. 



but, on many accounts, are deserving of the most serious attention 

 of the physiologist and naturalist. Instead of displaying the 

 ordinary cysticercal form, characterized by the head, neck, and 

 body, etc., the vesicle retains throughout its life-changes a more 

 or less globular or oval figure. In the earliest stages at which it 

 has been observed, the juvenile hydatid is perfectly spherical, and 

 is invariably surrounded by a capsule of condensed connective tissue 

 formed from the organs of the host. As shown in the accompany- 

 ing illustration (Plate XIII., Fig. 1) the vesicle after removal from its 

 capsular covering, consists simply of a thick laminated membrane, 

 forming the so-called cuticle or cuticular layer, and an inner granu- 

 lar mass, which subsequently becomes enveloped by a dehcate trans- 

 parent granular membrane. At the fourth week, the echinococcus 

 capsule measures about the ^ of an inch in length, its contained 

 hydatid being little more than the half of this diameter. Its sub- 

 sequent growth is by no means rapid, seeing that at the eighth 

 week the hydatid has attained only the ^" or thereabouts. At this 

 period, Leuckart shows that the internal or granular mass deve- 

 lops a number of nucleated cells on the inner surface of the so- 

 caUed cuticle. These cells, which are at first rounded or oval, 

 become angular or elongated in various directions, and, even, dis- 

 tinctly stellate ; in this way a new membrane is formed, consti- 

 tuting the so-called inner membrane or granular layer. The inter- 

 mediate stages between this condition and that of the mature or 

 fuUy-formed echinococcus hydatid have not, so far as I am aware, 

 been satisfactorily made out. This partly arises from the circum- 

 stance that the echinococcus heads are only developed from the 

 internal membrane after the expiration of a considerable lapse of 

 time. Leuckart, in his fourth experiment, hoped to have found the 

 heads (scohces) developed within the vesicles, but although nine- 

 teen weeks had elapsed since the time of feeding, and the hydatids 

 were about as large as nuts, no trace of heads could anywhere be 

 found. It becomes evident, therefore, that many months must 

 elapse before echinococci are developed within our bodies after we 



