THE TAPEWORMS {CESTODA) OF THE EED GROUSE 337 



size : the largest forms are about as long as the rostellar hooks, i.e., Q'Qfx ; the 

 smallest forms ai-e perhaps half this size, and there are intermediate sizes. Each 

 hook is slightly curved and tapers to a fine point, each possesses a " heel " which, 

 as is shown in PI. LI., Fig. 2, is developed in a varying degree. In many cases the 

 proximal end resembles the "head " of a thigh-bone. The hooks are arranged in 

 a ring, but the ring contains no definite and regularly arranged rows, rather it 

 is a small circular forest or hedge of hooks of varying sizes and shape. 



The head is usually followed by an unsegmented neck, three or four millimetres 

 in length, but I have seen one or two specimens in which the segmentation occurs 

 immediately behind the head. In transparent specimens longitudinal muscles 

 running to the suckers can be seen traversing the neck. In most specimens the 

 reproductive pore is on one side of the body throughout its entire length, but in 

 others, more rare, it changes over, and having been for the anterior half of the body 

 on the right side it suddenly passes to the left and remains there till the end. 



The number of the proglottides varies with the length of the worm. An average- 

 sized specimen would have between two hundred and fifty and four hundred 

 proglottides ; each of these might contain, say, a couple of hundred eggs. These 

 figures, though necessarily rough, give some idea of the number of ova a single 

 tapeworm may contain at any one moment. But mature proglottides are always 

 breaking away, and fresh ones are always being formed, like the ciphers of a 

 recurring decimal, so that the number of ova a tapeworm produces in the course 

 of its life is very much greater than the number it contains at any one moment. 



Although the male and female reproductive openings are close together, the 

 male orifice is very clearly anterior to that of the female. It leads into a muscular 

 protrusible penis, which was in all cases retracted. The penis ends in a much 

 coiled vas deferens, which runs slightly obliquely half across the proglottis, near 

 to the anterior edge ; here it ends in a number of diverticula which form the testes. 

 These are scattered throughout the parenchyma. The wall of the vas deferens 

 is thin, its lumen is spacious, and it acts as a vesicula seminalis. The lumen is 

 lined by a thin cuticle, and outside this and all around it are a number of spherical 

 or oval cells which, without exactly forming an epithelium, probably secrete the 

 cuticle. 



The vagina opens immediately behind the vas deferens. Its outermost part is 

 thick-walled, and the lumen contains some homogeneous substance which 'stains 

 deeply ; further on the wall becomes thinner, the lumen more capacious, and here 

 masses of spermatozoa are to be seen. The ovaries are two, right and left, each 



VOL. I. Y 



