PKESERVATION OF THE EGGS OF HELMINTHES 



111 



but are furnished with a covering, composed of rods arranged radially, 

 (fig. 34), which is derived from the substance of the embryo itself. 

 The oncospheres are easily obtained by pricking or teazing out ripe 

 proglottides from the Tsenia varieties given above. 1 Eggs covered 

 with a thin colourless shell, to which one or two filaments are 

 attached, are found in the uterus of younger proglottides (fig. 35). 



The eggs of other Tgenia varieties, when taken from ripe pro- 

 glottides, also contain fully developed oncospheres. But the shells 

 and embryonal coverings vary in form and number as well as in their 

 arrangement, the different orders and species presenting considerable 



FIG. 35. Egg from the uterus of Tcenia 

 , Gze. Thin shell with filaments. In 



FIG. 34. -a, Oncosphere (so-called T *v, TliT 



enia eee\ of Tania afrir,. n. \ T lS f,w .. the centre ls . the ball-shaped oncosphere, sur- 



Tsenia egg) of Tcenia african,a v. Lstw., 

 surrounded by the embryonal covering. 



rounded by the embryonal covering with radial 



VWftAWVUMW *^T W-Ut* OJ.X.1.U1. V \JllCb 1 UV/W&AJJK* -, . rl ,, -. 11 1 1 J -1 j 1 



b, Free oncosphere of Dipylidium cani- markings The large cells between it and the 

 m*m(L.). (Magnified.) egg-shell form a second embryonal covering. 



The granular mass to the right is composed 

 of yolk-granules. 500:1. (After Leuckart.) 



diversity. An interesting example is provided by the "cucumber" 

 tapeworm (Dipylidium caninum), whose eggs, when taken from the 

 ripe proglottides, are arranged in bundles (fig. 36). 



There is also considerable variation among the eggs of Bothrio- 

 cephalides. As a general rule, species with the genital openings 

 upon the flat surface of the body have eggs which resemble those 

 of the endoparasitic Trematodes, the oncospheres being undeveloped 

 even in ripe excreted proglottides (fig. 37). Those species, on the 

 other hand, which have their genital openings at the edge of the 

 body surface, form thin- shelled, lidless eggs, in which the embryo is 

 fully formed before the eggs are deposited. 



There is a similar diversity among the eggs of Nematodes. Thus, 



1 Care must be taken to guard against infection when working with ripe pro- 

 glottides of T. solium and T. saginata of man, as man may also serve as the inter- 

 mediate host for the development of the oncospheres into Cysticerci. Similarly, 

 precautions should be observed when making the post-mortem examination of dogs, 

 as the oncospheres of T. echinococcus will also develop in man. This worm is very 

 small and very difficult to find, as it conceals itself between the villi. 



