PLATYHELMIA. 41 



and narrow, while at the other extremity they attain the length 

 of half an inch and about two-thirds that breadth. The scolex 

 is slightly, the proglottides very much flattened dorso-ventrally, 

 but there is no obvious difference between the dorsal and ventral 

 surfaces. The somewhat pear-shaped scolex bears four muscular 

 suckers on its broadest part, and at its free head-end there is a 

 round projection (the rostellum), in which are imbedded some 

 twenty-four chitinous hooks, arranged in a double circlet. By 

 means of these hooks and suckers the tapeworm firmly fixes 

 itself to the wall of the intestine. The difference in size between 

 the proglottides is accounted for by the fact that they are not all 

 of the same age, those next the scolex being youngest. In fact, 

 during the life of the scolex, new joints are continually being 

 developed by the alternate constriction and growth of its narrow 

 neck-end. A proglottis taken from about the middle of the 

 body will be found to possess a complicated set of hermaphrodite 

 reproductive organs, while the oldest proglottides are full of eggs 

 containing embryos. About the middle of one edge of a proglottis 

 is seen a small elevation, the genital papilla. These papillaB are 

 alternately right and left in successive proglottides. As new 

 joints are developed at the head-end old ones become detached 

 and pass out of the body of the host. No sexual organs are 

 found in the scolex, which is often regarded as an asexual indi- 

 vidual from which, by means of budding, a chain of sexual 

 individuals (proglottides) arise. It is, however, more likely 

 that the entire worm is a single individual. 



The tapeworm is entirely devoid of digestive organs, its food 

 consisting of the highly nutritious ready digested material with 

 which it is surrounded, and which can readily diffuse into its 

 body. Although the animal is invested by a complex four- 

 layered cuticle this does not prevent such diffusion, as the two 

 outer layers are traversed by numerous pores. Below the cuticle 

 there is an epidermis composed of a single layer of spindle-shaped 

 cells. The hooks in the head are cuticular thickenings. 



Excretory Organs are present similar to those found in the 

 Liver-fluke. Like the other internal structures these are imbedded 

 in a mass of parenchyma, which serves as a kind of packing-tissue 

 and is made up of variously shaped cells and a granular matrix 

 through which detached nuclei, fat-globules, and calcareous par- 

 ticles are scattered. A main excretory tube runs along each side 



