subject permits, and briefly summarised tlie matter as fol- 

 lows: — 



What is known as tbe hydatid cyst is really the cystic or 

 bladder-worm phase of development of a minute tapeworm 

 which inhabits the upper j^art of the small intestine of the dog. 

 Three varieties of the hydatid have been described, viz., the 

 Acephalocystic form, where no scolices or daughter-cysts are 

 found ; the variety called Echinococcus Scolicipariens, where 

 brood-capsules and scolices are present ; and finally, Echino- 

 coccus Altricipariens, where daughter-cysts are developed. 

 There are good reasons, however, for the opinion that these 

 forms do not mark distinct species, but merely variations of one 

 species. I may remind you also of the remarkable transmuta- 

 tions and transmigrations undergone during the complete life- 

 cycle of this parasite ; how the adult tapeworm inhabits in great 

 numbers the small intestine of the dog, but in which animal the 

 hydatid cyst has never been found; that the last joint filled 

 with ripe ova passes from the intestine of the dog into the 

 outer world, and that the eggs are conveyed by the various ex- 

 ternal forces of nature into drinking water, and that they are 

 scattered on grass and herbage ; that the egg becomes swal- 

 lowed by some herbivorous animal or by man, and that then 

 the egg-shell becomes digested in the stomach, thus releasing 

 the six-hooked boring embryo formerly enclosed within it. 

 That the embryo begins at once to bore its way into the coats of 

 the stomach until it reaches the inside of a small blood vessel, 

 where it is caught in the current of blood, and conveyed to the 

 capillaries of the portal system within the liver ; here the 

 majority rest and develope into hydatids. Some of them, how- 

 ever, pass through the capillaries of the liver and enter the 

 general and pulmonary circulation. In this way it follows that 

 an}' organ of the body may become the resting place of an embryo, 

 which proceeds to continue its development into a hydatid. 

 We shall find from the statistics of the disease that the 

 lungs, heart, brain, spleen, kidney, muscles, and bones are all 

 liable to be attacked, although by no means in a like propor- 

 tion. The six-hooked embryo then proceeds to change into a 

 hydatid cyst. This in turn produces by a process of budding 

 the Echinococci. The Echinococci when transplanted into the 

 small intestine of the dog develope into the Scolices. These now 

 form joints, two or three in number, and the last one of these 

 contains the ripe eggs. To such curious series of • changes 

 Steenstrup gave the name of the "alternation of generations." 

 In sheep and oxen the cystic form of the parasite exists in 

 the liver, lung, and other organs ; but they never liave the 

 little tapeworm in the bowel. The hydatid lives, not on 

 chyme, as the tapeworm does in the intestine of the dog, 



