16 



and circlet of spines retracted or exserted. The former con- 

 dition alone is that in which I have observed this animal in 

 the fresh state. The other form 1 have myself only met with as the 

 apparent consequence of incipient decomposition, and it has seemed 

 to me to have arisen under these circumstances, from the imbibition 

 of fluid swelling the body of the animal. 



In the more usual state, or that in which the head is retracted with- 

 in the body, the vermicule presents an ovoid form, flattened at the 

 poles, and having a depression or notch more or less evident at each, 

 (fig. 2.) The depression at the anterior cephalic or unattached extre- 

 mity, is the orifice of a canal leading into the middle of the body, and 

 by which the head with the circlet and hook is protruded. The dou- 

 ble line proceeding from this orifice divides into two branches in the 

 centre of the body, as is seen in the figures, and below this division 

 is the circlet of spines on the retracted head. At the opposite poste- 

 rior, caudal, or attached extremity of the body, the depression marks 

 the place of insertion of the pedicle ; it may be observed that this 

 pedicle appears to perforate the outer tunic of the body and to be 

 continuous with the granular matter in its interior. 



I have not given any figure of the Echinococcus with the head pro- 

 truded, as I believe they never occur in that state in the attached 

 masses, and only when the animal has been spontaneously detached 

 and perhaps farther developed, or as the effect of changes indicative 

 of commencing decomposition. M. Livois' description of it, which is 

 very accurate, states that " It is transparent throughout its whole ex- 

 tent, and about the middle of its length it exhibits almost always a 

 sort of contraction, which separates into two portions. One posterior, 

 more slender, which may be considered as its caudal vesicle; the 

 other anterior, more swollen, upon which are placed the important 

 organs of the little animal, viz., the hooks and suckers, and this may 

 be regarded as the head of the worm." 



This extremity is terminated by a hemispherical point, transparent 

 and imperforate. The base of this elongated extremity or proboscis 

 is surrounded with a double row of spines or hooks, which precisely 

 resemble those of the Tania and Cysticerci, and are falciform, with 

 a process or apophysis on one side, probably for the attachment of 

 a motor muscle. They are very sharply pointed, and some are larger 

 than others, and the longer ones are those of the anterior row, and the 

 hooks of each row are placed alternately. The arrangement of these 

 spines is precisely the same in the Echinococcus of man and of ani- 

 mals." With reference to this point of the anatomy of the Echinococ- 



