CEYLON PEARL-INDUCING WORM. 125 
_A pearl is therefore the sarcophagus of a parasite, whose nearest 
relations include human and other animal tape-worms, all varieties 
of human hydatids (or Echinococcus), as well as those parasites 
which cause the ‘“‘ stagger disease ” in sheep and goats, &c. 
The normal and typical life-history of Cestodes in general is toe 
well known to require full repetition here. The adult worms occur 
exclusively in vertebrates (with the exception of Archigetes, which 
may become adult in the ccelom of 7'ubifex), where they inhabit the 
internal organs. The larva or cysticercus may occur either in an 
invertebrate or in a vertebrate. The transference of the larve to 
the final host takes place quietly, during a meal. Thus, the larvee 
of Tenia solium occur in the tissues of the pig. If present, and if 
the flesh of this animal is eaten by man in an improperly cooked 
condition, the larvee become adult tape-worms in the human intestine. 
From these adults, eggs are passed out in the foeces, and the omni- 
vorous habits of the pig lead to the re-infection of this animal, and 
thus the cycle goes on. Homologous stages of T'enia serrata occur 
between dogs and mice, and many other instances might be cited. 
The life-history, however, is not always of this type. In Hymeno- 
lepis murina both stages occur in the rat without the intervention 
of a second host, the larve inhabiting the villi and the adult worm 
the intestinal cavity of the same animal. Such a life-history is said 
to occur in Hymenolepis nana found in man. 
The larve of Bothriocephalus latus probably first enter some 
invertebrate host, and are then eaten by a pike or trout. If the 
infected fish are eaten by man, the parasites develop in the intestine 
into adult worms, which often attain a length of 30 feet. There 
are thus three hosts. With reference to this particular tape-worm, 
it is interesting to note that the primary larve are the only larve in 
the group Cestoda known to be ciliated. ; 
Further complications in the life-history of Cestodes are also 
known. Thus, 7'enia solium is found adult in man. “The danger of 
its presence in the body of man, or in the flesh of the pig, lies in the 
fact that the larva or bladder worm (known as Cysticercus cellulose) 
can live in the most varied organs. Thus, if by accident a mature 
proglottis be eaten, the embryos bore their way into the wall of the 
stomach, and entering the portal vein may reach in time the muscles, 
the brain, the eye, or even the heart itself, and attain the cystic 
condition. Even more disastrous may be the result should some 
ripe joints of a mature worm work their way from the intestine 
back to the stomach. Should this happen (and though it has not 
been directly proved, the possibility is to be reckoned with) the 
result would be the release of vast numbers of embryos capable of 
inflicting fatal injury on the host. An abnormal Cysticercus of 
this species is probably Tenia (Cysticercus) acanthotrias, Weinl.* 


* Gamble: ‘‘ The Cambridge Natural History.” Worms, Rotifers, and 
Polyzoa, p. 79. 
