102 THE TAPEWORM 



oviducts which unite and open into a region surrounded by the shell 

 gland. The ducts from the yolk-glands, and from the uterus, which 

 is eventually distended with eggs and embryos, also open into this 

 region, and from it the vagina leads to the outside by way of the 

 genital pore. A seminal receptacle may be formed as a distended 

 region of the vagina. Make a large drawing to show the features 

 observed. 



Exercise 3. — The Six-hooked Embryo. 



(e) In the mature proglottids the uterus is distended with eggs and 

 embryos and only remnants of other parts are found. Each zygote 

 is enclosed in an eggshell, together with yolk cells of which there are 

 four in most cestodes. Within the uterus these zygotes develop into 

 six-hooked embryos. Place in a watch glass containing a little water 

 a mature proglottid, from a fresh specimen of the worm or from one 

 preserved in formalin, and tease the proglottid into bits. Mount on 

 a slide a little of the siltlike material thus liberated from the uterus 

 and examine with the highest powers of your microscope. The em- 

 bryos are now seen encased in their shells. What is the nature of 

 these eggshells? Can you find the six hooks? Force embryos out of 

 their shells by pressing gently on the cover glass with a needle. Can 

 you make an estimate of the number of six-hooked embryos produced 

 by a single proglottid; by the entire worm in the course of its life- 

 time? Draw (3-5 X projected size), showing these features. 



Exercise 4. — The Bladder- worm. 



(f) The mature proglottids, with their six-hooked embryos, are 

 detached and pass out with the feces of the host. The six-hooked 

 embryos are then liberated by the rupture or disintegration of the 

 proglottid and enter the secondary host with its food. After the shell 

 disintegrates in the digestive tract of this new host, the six-hooked 

 embryo bores through the mucous membrane into the submucosa and 

 by entering blood vessels may be carried to tissues remote from 

 the digestive tract. Within the tissue where it comes to rest the six- 

 hooked embryo develops to a stage known as the bladder-worm. 

 Examine living or preserved bladder-worms, and make out the scolex 

 and neck, and their position with respect to the bladder. When the 

 flesh of the secondary host, containing the bladder- worms, is eaten 

 by the primary host, the scolex and neck are everted, the scolex be- 

 comes attached to the mucosa of the primary host, and the remnant 

 of the bladder becomes digested. Soon the neck begins to grow and 



