TiENIA SOLIUM. 221 



proglottis sooner or later to burst, and the embryos thus become 

 dispersed ; some are thus 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 is furnished with a special 

 boriug apparatus, having at its anterior end three pairs of hooks ; 

 the entire group of embryos of any single proglottis is consequently 

 called the " six-hooked brood." After a while, by accident, as it 

 were, a pig coming in the way of these embryos or of the proglot- 

 tides is liable to swallow them along with matters taken in as food. 

 The embryos, immediately on their being transferred to the digestive 

 canal of the pig, escape the eggshells and bore their way through the 

 living tissues of the animal, and having lodged themselves in the fatty 

 parts of the flesh, they there rest to await their further transfor- 

 mations or destiny. The animal thus infested become measled, its 

 flesh constituting the so-called measly pork. In this situation the 

 embryos drop their hooks or boring apparatus and become trans- 

 formed into the Gysticercus cellulosce. A portion of this measled 

 meat being eaten by ourselves, either in a raw or imperfectly 

 cooked condition, transfers the Gysticercus to our own alimentary 

 canal, in which locaHty the Gysticercus attaches itself to the wall of 

 the human intestine, and, having secured a good anchorage, begins 

 to grow at the lower or caudal extremity, producing numerous 

 joints or buds to form the strobila or tapeworm colony. 



Thus the cycle of life-development is completed, and we have a 

 simple alternation of generation in which the immediate product of 

 the proglottis (or sexually-mature zooid-individual) is a six-hooked 

 brood ; by metamorphosis the latter becomes transformed into the 

 Gysticercus, having a head with four suckers, and a double crown 

 of hooks ; and by gemmation the latter gives rise to a whole colony 

 (strobila) of individuals, the greater part of which are destined to 

 become sexually mature zooid-individuals, or proglottides. It 

 will be observed, therefore, that the product of a single ovum 

 is, in the first instance, a single non-sexual embryo ; in the 



