T^NIA ECHINOCOCCUS. 259 



have swallowed the proper tapeworm eggs and their contained 

 embryos. 



In regard to the subsequent changes which, in due time, bring 

 about the development of the sexually mature Tcenia echinococcus, 

 I need not say much, nor need I dwell on the ancient opinions 

 entertained by Rudolphi, Roll, and others, that these little tape- 

 worms were the young of the Tcenia cucumerina, T. serrata, and 

 other well-known cestode species. It must suffice me to indicate the 

 present position of our knowledge as regards points of importance 

 only ; and here, therefore, I may at once remark, that Yon Siebold 

 was the first to breed these tiny tapeworms by the experimental 

 method. Many other helminthologists have since verified his results, 

 amongst whom, of course, Kiichenmeister, Haubner, and Leuckart 

 have played a most conspicuous part. I have myself several times fed 

 dogs with echinococci derived from sheep, and also from the human 

 subject ; but, for some unexplained reason or other, this series of 

 experiments has only yielded negative results. I mentioned 

 this to Leuckart, who expressed surprise, and could only account 

 for my non-success by the supposition that the food subsequently 

 supphed to the animals had been unsuitable, or had acted 

 anthelmintically. According to Kiichenmeister, a period of eight 

 or nine weeks is required for the development of the administered 

 echinococcus-heads into sexually mature tapeworms, but Von Sie- 

 bold and Leuckart found them full grown in seven weeks. Their 

 especial haunt is the duodenum and upper part of the small intes- 

 tines, in the mucus of which they lie embedded with their heads 

 attached to the villous surface of the gut. The milk-white appear- 

 ance of the joints betrays their presence, but they may bo easily 

 overlooked, especially if they happen to be only incompletely 

 developed. 



Hydatids. — Although I have already briefly described the prin- 

 cipal developmental phases of the Echinococcus tapeworm, the 

 importance of this subject, in a medical point of view, demands a 

 more particular account of hydatid formations. At the outset 



