308 THE ANATOMY OF CESTODES. 



better to examine the younger proglottides, whose ovaries are still 

 without eggs. In the older joints, in which copulation has taken 

 place, and the embryos are perhaps already developed, the testicular 

 sacs are generally empty and deserted, and sometimes have even in 

 great measure disappeared. Even the cirrhus and cirrhus- pouch 

 often fall into decay (Fig. 160, B). 



This unequal development is most striking in the Tseniadae, which, 

 having no uterine opening, are unable to void their eggs successively, 

 and form them indeed only during a relatively short space of time, 

 whilst the Bothriada3 go on depositing during their whole life, as long 

 as they remain in the intestinal canal of their host, and thus require the 

 spermatic elements during a longer time. In this way it also becomes 

 clear that the Bothriadae not only continually replace the externally 

 deposited eggs by new batches, but as time goes on collect larger and 

 larger numbers in their uteri, which, while still in the neighbourhood 

 of their place of formation, distinctly exhibit the characteristics of 

 their youthful stage. On the contrary, the number of eggs in the 

 Tcenice is not increased after the transference has once taken place into 

 the uterus. And as this transference, as already mentioned, only lasts 

 during a definite and relatively short period, the eggs in the interior of 

 the uterus are all of nearly the same age, and of the same or only slightly 

 different development. 1 And this is all the more surprising in these 

 animals as the development of their eggs goes much further than in 

 the case of Bothriocephalus, and only terminates with the formation of 

 an embryo. When the uterus is filled, the female germ-producing 

 organs of the Tcenice have fulfilled their function, just as have the testes 

 after the filling of the seminal duct, and are then gradually destroyed 

 by the pressure of the uterus, which becomes larger and larger during 

 the embryonic development of the eggs. In the investigation of the 

 generative organs in Tcenia, the smaller " unripe" joints must evidently 

 be examined, for in the so-called " ripe " or pregnant proglottides 

 these parts are only slightly present, or have even entirely dis- 

 appeared. 



1 Sommer declares (loc. cit., p. 532) my statements, that "in the case of the Tcenia; 

 the transference of the eggs into the uterus is limited to only a short space of time," 

 and that consequently "the eggs of a uterus are always of nearly the same age, and 

 of similar or only slightly different development," to be erroneous. He bases this asser- 

 tion on the fact that the transference of the egga in Tcenia sayinata takes place over a 

 stretch of 300 to 400 proglottides, and that the eggs of the older proglottides in the posterior 

 end of the uterus stem differ considerably from those found in the side branches. I have 

 known these facts from my own experience, and for a long time, but, notwithstanding, I 

 think I am able to support my statements. For Sommer overlooks that the matter in 

 question was not the nature of the Taeniadae per se, but the contrast between it and that of 

 Eothriocephalus, and I still think that this contrast was perfectly accurately and naturally 

 characterised in the way I put it. 



