210 
Strongylus polygyrus 
separate origins and extend almost to the margin of the bursa. The lateral 
rays arise from a common trunk and are divergent; the postero-lateral ray is 
Fig. 1. Heligmosomoides polygyrus. Posterior extremity of female, lateral view, x about 220, 
bu. 
i 
i 
Fig. 2. Heligmosomoides polygyrus. Head, with cuticular expansion, x about 650. 
only slightly thicker than the externo-dorsal and runs almost parallel with it, 
the medio-lateral and extern o-lateral rays are considerably thicker than the 
