FAMILY T^NIAD^E. 



391 



FAMILY I., 



The small pear-shaped or spherical head bears, at some distance from 

 the apex, four roundish suckers, which are situated at tolerably equal 

 distances from one another, and possess a powerful musculature of their 

 own. Between the suckers there is usually, near the apex, a simple vr 

 manifold circle of claw -like hooks. To support and move the latter, 

 there is a capsular muscular apparatus the rostellum which pro- 

 trudes more or less from the crown of the head, sometimes even resembling 

 a proboscis, which can also be retracted. 



The proglottides are distinctly separated from one another ; in their 

 adult state they are usually longer than broad, and are almost always 

 provided with marginal generative openings, 

 sometimes confined to one side, sometimes alter- 

 nating irregularly on both sides. In some cases 

 also the joints have a pore on either side. The 

 number of sexual joints varies greatly (from three 

 up to three or four thousand} ; the length of the 

 adult tape-worm is, therefore, also subject to much 

 variation. The liberation of the proglottides takes 

 place with great regularity, but somewhat late, 

 after the embryos are almost fully formed. The 

 uterus has no direct communication with the 

 exterior, so that the eggs remain inside the pro- 

 glottides, and are only set free when these are 

 destroyed. 



The yolk -glands are but slightly developed. 

 During development the embryos, while increasing 

 continually in size, become surrounded with an 

 often multiple envelope of more or less firmness. 



Since the transference of the eggs into the uterus FIG. 227. Head of Tcmia 

 is restricted to a comparatively short time, one sohum - ( x 35 -) 

 finds them almost all at the same stage of development. 



In the adult state the Tseniadee live especially in terrestrial animals 

 mammals and birds while the larval forms (bladder- worms, or 

 Cysticerci) are found in very diverse higher and lower animals. They 

 possess, with few exceptions, a well differentiated caudal bladder, 

 but show manifold peculiarities as regards their proliferation. Some- 

 times they form distinct polycephalous colonies. Those occurring in 

 the mammals usually attain a considerable size, which is largely due 

 to the copious accumulation of watery fluid in the bladder. 



