568 



TJENIA MARGIN ATA AND CYSTIC ERCUS TENUICOLLIS. 



In regard to the differences in size, we must note that Tcenia 

 marginata liberates the largest and T. coenurus the smallest proglot- 

 tides. Those of the latter measure (without pressure) 5 to 6 mm. long 

 by 2'5 mm. broad ; in the former, the size is almost double (9-11 mm. 

 by 4-5 mm.). The proglottides of T. serrata are intermediate in 

 dimensions, and measure 8 mm. by 3 mm. 



The structure of T. marginata has been already described. T. 

 serrata has more lateral branches (8-10 on each side), and a richer 

 and more irregular ramification. In T. ccenurus the number ascends to 

 from twenty to twenty-five, but they are somewhat simpler and shorter. 



FIG. 308. Form of the uterus in different tape- worms. A, in T. terrata ( x 4) ; 

 , in T. marginata ( x 6) ; C, in T. coenurut ( x 10-15). 



The eggs of the three species have a somewhat oval form, and are 

 almost equal in size, having a clear average diameter of 0*027 mm. 

 There are of course various divergences in points of detail, and 

 perhaps the eggs of T. coenurus are, on the whole, somewhat larger. 

 The embryonic shell has the familiar appearance, but its thickness, 

 especially in the case of T. ccenurus, is markedly inferior to that of 

 the eggs of the human tape- worm. In the size of the embryo and its 

 hooks these species are clearly allied to T. solium; in fact all the 

 cystic tape- worms (of the group Cystotcenia) differ in this respect only 

 in unimportant details. 



Of course it is not only the free proglottides which thus differ 

 from one another, but also the " ripe " joints. Their number varies 

 not inconsiderably in the different species, the extremes being again 

 T. marginata, with not unfrequently fifty, and T. ccenurus, with hardly 

 ever more than a dozen. 



It is evident that these differences must contribute to the above- 

 mentioned differences in size of the tape-worms of the dog. But 

 they are not the only factors affecting the latter. We must also 



