782 PARASITIC DISEASES. 



the Bothriocephaliis the uterus has the form of a rosette, whereag 

 in the Taenia it is usually tree-like, and by counting the number 

 of uterine branches we are often able to determine the species. 

 At the same time the sexual openings can be observed — (1.) On 

 the margin, and alternately right and left, i.e., on the left margin 

 of one segment, on the right margin of the next, on the left 

 margin of the third, and so on, e.^., Tccnia coenurus, Tcenia serrata, 

 Tcenia marginata, and most Tcenice ; (2.) Two marginal openings 

 for each segment, one on the right margin and one on the left 

 (only in Tcenia cucumerina and Taenia expansa) ; (3.) Openings 

 not marginal, but in the middle of the ventral surface, e.(/., 

 Bothriocephaliis. 



If the eggs from the uterus of a ripe segment of a Tamia 

 be examined, they appear to the naked eye as coloured points, 

 and under the microscope as round or oval bodies. The shell is 

 thick, and is seen to consist of little prisms cemented together. 

 In the interior of the shell the embryo is visible as a little solid 

 body provided with six hooks. The eggs of the Bothriocephaliis 

 present quite a different appearance. 



These eggs are hatched when they gain access to the ali- 

 mentary canal of a suitable host, which is rarely the same as 

 the host of the adult Tcenia. Stimulated by the warmth and 

 acted upon by the gastric juice of the alimentary canal, the shell 

 is more or less dissolved, and the six-hooked emhryo or Proscolex 

 becomes free. Helped by its hooks, the embryo bores its way 

 through the wall of the alimentary tract, and is carried along 

 with the blood, or otherwise, to some place suited for its further 

 development, it may be the connective tissue, muscles, liver, 

 lungs, or even the brain, as is the case with the Ccenuriis 

 cerebralis in the brain of sheep. Having reached a suitable 

 resting-place, the solid embryo drops its hooks, and, actii)g as a 

 foreign body, causes local exudations and new formations of 

 granular matter and connective tissue. Thus the surrounding 

 tissues form nutritive material and a connective tissue capsule 

 for the solid embryo. The embryo, fed at the expense of the 

 surrounding tissues, rapidly grows in size, loses its solid character, 

 and becomes a hollow sac filled with fluid. In this condition 

 the creature is spoken of as a cystic or bladder-worm, or more 

 commonly as a measle or hydatid, and this cystic stage is quite 

 comparable with the sporocyst of a trematode-worm. The cystic* 



