448 



GROWTH AND STEUCTURE OF T^NIA SAGINATA. 



behind the other. The latter is seen to be in connection with the 

 lower end of the uterus. Similarly, one can distinguish the efferent 

 ducts of the ovary and the yolk-glands. 



From this stage there is but a step to the perfect development 

 of the generative organs. All the parts are present ; the difference 

 is only formal, and the gradual development of the succeeding joints 

 requires no special discussion. 



The development of the generative organs is not, however, com- 

 plete with the formation of the eggs and egg-glands ; for the Tmnim 

 are, as is well known, distinguished from the other Cestodes in that 

 they only produce eggs and spermatozoa during a comparatively short 

 time, and not merely are the eggs fertilised, but the embryos proceed at 

 once to develop in them. After the sexually mature joints there 

 follow others, which may be termed " pregnant," and this pregnancy 

 induces a further series of changes. 



At the period of sexual maturity the uterus is a straight canal of 

 comparatively small calibre. Its capacity is too small for the great 

 multitude of eggs, and the more so since in the Tcenice the latter grow 

 during development to many times their original diameter. The 

 uterus therefore begins to adapt itself to the requirements of the 

 pregnant animal. Very soon after the transference of the first eggs 



it not only increases in length, but entirely 

 changes its originally simple shape by the 

 formation of lateral branches. The walls 

 of the uterus give rise to small protube- 

 rances, which grow with ever-increasing 

 rapidity, here and there bifurcate, and form 

 secondary twigs, and finally fill up the 

 whole breadth of the median portion as far 

 as the longitudinal vessels. The branches 

 are at first long and thin, and differ from 

 their subsequent state in being longer in 

 correspondence with the broad and short form of the joints, and also 

 in diverging but slightly from the transverse direction. 



For a while the male and female reproductive organs can still be 

 seen beside the branches of the uterus. But the more the latter 

 increase, the more the former retreat from observation. This is not so 

 much because they are covered by the lateral branches, but is mainly 

 due to the gradual degeneration which ensues at the close of their 

 functional activity. This disappearance is gradual, and is not uniform, 

 so that even in a perfectly ripe joint, remains of the reproductive 

 organs may still persist. The female germ-producing organs persist 



longest, and the shell-gland so long that the development of the 

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Fig. 255.— Formation of the 

 first lateral branches of the 

 uterus. (x5.) 



