EXPERIMENTS WITH TAPEWORMS. 305 



transferred to the intestine of a second or definitive host. If this 

 transfer is not made development stops, after a time death ensues*, 

 and degeneration of the young tapeworm takes place. However, 

 if it reaches the intestine of the definitive host, barring accidents, 

 it evaginates the already formed scolex, attaches itself to the 

 mucous membrane by hooks or suckers, grows to maturity, 

 reproduces hermaphroditically, and to complete the life history 

 all that is needed is for the eggs to reach again the particular 

 kind of individual that may serve as an intermediate host. 

 This is of course a matter of common knowledge. 



In order to fully understand the experiment it will be best 

 to call to mind something of the structure of a cysticercus and 

 the transformation which takes place when it reaches the in- 

 testine. Fig. i is a drawing made to show the general structure 

 of a mature cysticercus taken from a half-grown wild rabbit. 

 It is still enclosed within the cyst. When taken from the ab- 

 dominal cavity a cysticercus consists of a whitish, elongated 

 bladder-like structure filled with a watery fluid; at the smaller 

 end is a dense, compact mass of tissue. Examination shows that 

 this more solid portion of the bladderworm is due to an invagi- 

 nation of the anterior end as shown in Fig. 3. Within the 

 cavity of the invagination is found the apparatus, the scolex, 

 which serves for attachment to the walls of the intestine. In this 

 case the scolex is provided with both hooks and suckers. A few 

 hours after a cyst has been eaten by a dog, a young tapeworm, 

 already transformed, may be taken from the intestine. In this 

 process the invaginated portion evaginates, the scolex is everted, 

 and the bladder digests or is separated and lost in the faeces. 

 Fig. 2 is a drawing made from an evaginated cysticercus that was 

 treated with artificial digestive juices, and Fig. 4 is an enlarged 

 drawing of the scolex of the same. 



Now if Cysticercus pisifonnis is kept in physiological saline 

 (0.7 per cent. NaCl) it never or rarely evaginates. Fifty-five 

 specimens were left in such a solution for three days, in fact 

 until many had died, and at the end of that time only five had 

 evaginated. Besides this occasional evagination, one may 

 produce eversion of the scolex by careful physical manipulation. 

 Braun and Lu'he state that this can be readily done in the case of 



