Intestinal Parasites of the Dog. 309 



face, each of which becomes enlarged and hollowed out to form a 

 cyst which remains attached to the parent cyst by a short pedicle. 

 These are known as secondary vesicles, proligerous cysts, daughter 

 cysts, nurses, or brood capsules, and they need not develop 

 respectively their echinococcus heads or scolices. On the contrary 

 the first group of broad capsules, may each develop within it a 

 second group or generation (grand-daughter cysts), which in their 

 turn may produce (great-grand-daughter cysts). At any time in 

 the course of this development, these cysts or any one of them 

 (primary, secondary, tertiary, etc.) may develop from its internal 

 membrane the head of a taenia (scolex), the true larval echino- 

 coccus. Of these there are usually from 5 to 30 in the interior of 

 each proligerous vesicle, varying in size so as to suggest a differ, 

 ence in age. When developed the scolices are individually .19 

 mm. by .16 mm. in diameter, with a depression and orifice in the 

 free end showing where the head has become invaginated within 

 the sac. Thus it comes about that the hydatid, almost micro- 

 scopic at its start and with no apparent organization except a 

 simple chitinous membrane enclosing a clear or milky fluid, fin- 

 ally appears as a compound cyst, sometimes as large as an infant's 

 head, containing numerous heads or scolices, some attached to 

 the inner membrane of its parent sac, while others are detached, 

 dead, and float free in the liquid. 



Be-side the endogenous formation of proligerous cysts and scolices, 

 these sometimes develop outside the parent vesicle and hang from 

 its outer instead of its inner surface. These secondary external 

 vesicles are also formed from the internal parent membrane, but, 

 bulging outward, they rupture the external membrane and remain 

 pendant outside. They are more common in particular localities, 

 and animals, and in such cases the tendency appears to be to the 

 same form in a single animal, all being suggestive of a variety in 

 the parasite. The external vesicles are most common in rumin- 

 ants, pigs and men, and they rarely attain the same size as the 

 other forms. The internal vesicles are most common in man, pig 

 and horse, though also seen in oxen (Railliet). 



Still another development of echinococcus is known as E. Mul- 

 tilocularis, and characterized by the development of clusters of 

 minute cysts in size from a millet seed to a pea and mostly sterile. 

 Formerly called alveolar, colloid cancer these were identified by 



