THE ACTIVE SCOLEX. 81 



now the head with the neck seeks to extend itself, and this takes 

 place somewhat in the following way. The head, the hooks of 

 which still exhibit the position of cysticercal existence, that is, 

 with their apices directed backwards towards the suckers, and 

 their shafts towards the apex of the head, draws itself as it were 

 outwards through the neck, by turning itself inside out. 

 As a matter of course the whole worm is at the same time 

 as it were turned inside out ; and the margins of the head 

 and neck which were previously turned in, become the free 

 outer sides of the worm. At this moment, if we wished 

 to make a section through the anterior extremity of the 

 worm, we have to cut through not only two, but three 

 layers of the parenchyma of the body, the caudal vesicle, a layer 

 of the middle body, and the neck. During this turning the hooks 

 have generally retained their position, or have begun to acquire 

 that position of which I shall speak hereafter. From Leuckart's 

 experiments, in which he placed naked, but otherwise uninjured 

 cystic worms in a piece of the stomach of an animal at blood- 

 heat ; it appears that at the first, and indeed within five or 

 ten minutes after its introduction into this stomach, the worm 

 extended its head, feeling about as it were for a short time, whilst 

 it maintained a lively action with its suckers, and rapid peristaltic 

 movements with its caudal vesicle ; but immediately afterwards it 

 contracted it again within the neck and middle of the body, which 

 remain extended. In artificial digestion, this takes place until 

 the caudal vesicle is dissolved, which is done in from eight to 

 ten hours. In experiments by feeding, the worm is usually found 

 in the small intestine five or six hours after its administration ; 

 its head again extends and it attaches itself to the wall of the 

 intestine. The body and the collapsed, or more or less digested 

 caudal vesicle, 1 are now separated from the neck and head, and it is 

 often seen within the first twenty-four hours that the adhering 



1 When Leuckart enclosed a naked but uninjured Cysticercus in the small intestine of 

 an animal, he certainly saw the caudal vesicle collapse, but it was never digested, for 

 which a sojourn of one or two hours in the stomach was always necessary. If then a 

 Cysticercus be very rapidly driven through the stomach to the intestine, and espe- 

 cially if it be still enclosed in its enveloping cyst, similar circumstances may occur. 

 This was the case, at any rate, in those specimens described by me in the ' Prager 

 Vierteljahrschrift,' which I found in the intestine of a dog that died two hours and a 

 half after feeding, and which had a collapsed caudal vesicle, but had extended and 

 attached themselves, and still bore the enveloping cyst upon the collapsed caudal vesicle. 



I 



