STRUCTURE OF THE EGG. 449 



posterior uterine branches is not only retarded for a while, but their 

 form is also somewhat modified by its presence. The vacant space 

 between the posterior fan-shaped processes represents the position 

 occupied by the shell-gland. The unequal longitudinal development 

 of the uterus posteriorly and anteriorly is also associated with the 

 persistence of the shell-gland. 



B 



FIG. 256. Eggs of Tcenia saginata; A, Newly formed egg from the 

 uterus ; B, Ripe egg containing the embryo. After a drawing by Edouard 

 van Beneden. ( x 550.) 



As to the development of the eggs, I have but little to add to 

 what I have already said, which is partly based on investiga- 

 tions of Tcenia saginata. I content myself with noting that the size 

 of the embryo is about 0*02 mm. The shell which surrounds it is 

 distinguished by considerable thickness that is, length of the little 

 rods which are seated on it, and which attain their full development 

 after a very short period. Inclusive of this shell, the diameter of the 

 egg is on an average 0*03 mm., and its form is generally oval rather 

 than spherical. We have already noted that the eggs are also usually 

 still surrounded by the original vitelline membrane (0'07 mm.), 

 separated by an interval from the contents. Very frequently this 

 outer shell is drawn out at one or at two points into a more or less 

 long, thin, tail-like process, as is also frequently found in allied species. 

 This is still more constant in the newly formed uterine eggs, which 

 measure on an average 0*02 mm., and have usually a very distinct 

 oval form. The tails, which are almost as long as the eggs, always 

 spring from the poles. 



Malformations. 



There are but few tape-worms which exhibit such frequent and 

 various malformations as Tcenia saginata. Even the old observers 

 remarked some of them. But as at that time the two species of 

 large-jointed human tape-worms were not clearly distinguished, it 

 would be doubtful whether these observations referred to T. saginata, 



2 F 



