WORMS. 199 



The hooks, as seen under the microscope, form a regular circle, alternately big and 

 little claws. The suckers are very muscular, the fibres being arranged in two systems, 

 one equatorial and one meridional. Altogether the means are very 

 ample to secure the hold of the worm upon its abiding place. 



The proglottids, after their expulsion from the body of the host, 

 may be compared to the sporocysts of the flukes, for the eggs develop 

 into embryos within the proglottids, so that they become cysts filled 

 with larvae. " The growth of the multitude of embryos within their 

 interior causes the proglottis sooner or later to burst, and the embryos ^■'"f^^'J^^^^ °^ 

 thus become dispersed ; some are conveyed down drains and sewers, 

 others are lodged by the roadsides in ditches and waste places, whilst great quantities 

 are scattered far and wide, by winds or insects, in every conceivable direction. Each 

 embryo witliin the egg is furnished with a special boring apparatus, having at its anterior 

 end three pairs of hooks ; after a while, as it were by accident, some animal, a pig 

 perhaps, coming in the way of these embryos, or of the proglottids, swallows some of 

 them along with matters taken in as food. The embryos, immediately on being trans- 

 ferred to the digestive canal of the pig, escape out of the egg-shells, and bore their 

 way through the living tissues of the animal to lodge themselves in the fatty parts of 

 the flesh, where they await their further destiny. The flesh of the animal thus infested 

 constitutes the so-called measly pork. In this situation the embryos drop their hooks, 

 or boring apparatus, and become transformed into the Cysticercus cellulosaj. A por- 

 tion of this measled meat being eaten by ourselves transfers the Cysticercus to our own 

 alimentary canal, to the walls of which the larva attaches itself" (Cobbold). The 

 Cysticercus is the larva which infests the pig. Originally no helminthologist surmised 

 the existence of a genetic connection between the parasites in swine and the human 

 tape-worms. The great German zoologist von Siebold was the first to establisli the 

 exact metamorphoses, while Kuchenineister had the merit of clinching the proof by 

 experiment. 



• The life history of Tcenia solium illustrates the phases as they occur in nearly all 

 tape-worms infesting carnivorous animals. The cestods of the herbivores have a sim- 

 pler history, wliich we will relate directly. For the moment let us consider the more 

 complicated type of development : The eggs or embryos are dropped about, to be 

 swallowed by the first host, in which they assume the first or larval form ; the host is 

 preyed upon by some carnivorous animal, which, together with the flesh of its victim, 

 swallows some of the larvae, and these then undergo their final development. In order 

 to reach their ultimate abode the parasite must twice be swallowed by a host; it 

 accomplishes its migrations passively by the aid of the very animals it injures. The 

 larva is always a vesicular structure, a membranous sack with a little appendix, which 

 becomes the head of the adult worm. Imagine a glove of which the hand makes a 

 closed bag, and which possesses only a single finger; imagine also the tip of the finger 

 armed with a circlet of hooks and four suckers ; finally turn the finger in so that it 

 forms an inverted tube extending into the hand of the glove ; thus we can conceive a 

 good model of a Cysticercus ; the vesicle itself is about a quarter of an inch long, and 

 of a pale flesh color. Ordinarily the head is found turned in, but sometimes it is 

 everted, and eversion always takes place after the larva enters the intestine of its 

 second host. Now when the head is protruded the vesicle becomes the posterior por- 

 tion of the body, and the proglottids being developed behind the head, the tape-worm 

 is gradually formed in about three months by the continued interpolation of new joints 



