THE CESTOIDEA 103 



the intestine of its new host. The eggs are operculate, as in 

 Bothrioceplialus latus, and do not undergo any development till they 

 are laid. The six -hooked embryo is not ciliated, and feeding 

 experiments have thrown no light on the question as to how 

 the parasite gets into Tubifcx. In Ampliilina (39) the non- 

 operculate eggs are provided with a filament at one end, as in some 

 Trematodes. After a development resembling that of a normal 

 Cestode, an oval embryo issues (Fig. II. 2, 3) ; one half is ciliated, 

 and at the opposite end it carries ten hooks, which, curiously, are 

 precisely like those of the penis in number and shape. There are 

 also in Gyrocotyle ten hooks in the embryo. A group of unicellular 

 glands opens at the ciliated extremity, which have been regarded 

 with little justification as a remnant of the enteron. It is even 

 doubtful whether they develop into the glands which open into the 

 sucker of the adult. The fate of the embryo is unknown, as is also 

 the intermediate host. 



GRADE B. CESTOIDEA MEROZOA ( = Cestodes digen&ses, v. Ben. ; 

 = Cestoda polyzoa, Lang ; = Tomiosoma, Montic.). 



Cestoidea, in which the adult worm or " strobila" consists of two 

 distinct- parts, viz. (1) a sterile head or " scolex," provided with 

 organs of fixation ; and (2) a genital region or " body," in which 

 the genital organs are metamerically repeated ; and in most cases 

 this repetition is expressed externally by definite constrictions 

 separating the worm into " proglottids," each of which contains 

 usually one set of genital organs. These proglottids in most 

 cases drop off from time to time when mature. 



It will be convenient to describe a definite type, viz. Bothrio- 

 cephalus latus, in order to illustrate the anatomy of the Merozoa 

 in general. The "broad tapeworm" (Fig. III. 1) of man has a 

 wide area of distribution, but is limited to such peoples as employ 

 uncooked river fish as an article of diet, for in these fish, especially 

 the pike, the early stages of development are passed. 



The adult worm or " strobila " 1 consists of head or " scolex," 1 

 and a large number of short but broad segments or " proglottids." l 

 These are much compressed dorso-ventrally, and broader from side 

 to side than they are long, so that the worm has the form of a band 

 or ribbon, to which fact the technical name for the class is due. 

 The number of proglottids in R latus may be as many as 3000, or 

 even more ; and the length of the worm reaches 20 or 30 feet. 



The proglottids are not all of the same size or shape ; as the 

 proximal region (towards the scolex) is approached they become 

 narrower, and quite far forwards their dorso-ventral diameter or 



1 These terms were introduced by P. J. van Beneden, but Dujardin had already 

 used the term "proglottis " for the free, isolated, mature segment of Taeniae. Van 

 Beneden, however, used the word in a slightly different sense. 



