34 ILLINOIS BIOLOGICAL MONOGRAPHS [138 



and more anterior with respect to the first (Figs. 15, 37, 28). This might 

 indicate a stage in the disappearance of two papilla, giving way to the 

 more general condition of four cephalic papillae in the ascarids and fur- 

 thermore this would also make the bilaterality of the ascarid head more 

 pronounced. 



Often between the lips of the ascarid type the cuticula and parts of 

 the tissue lying beneath it are raised up into what has been termed inter- 

 labia. They fit nicely between the lips and where they are well developed 

 they have been misconstrued as extra lips. The size and form vary from 

 only small projections to a size subequal to the lips themselves as in Ascaris 

 nasuta Schneider and Ophidascaris mombasica Baylis. Other labial variations 

 arise by branchings of the pulp in each lip into diverse forms {Polydelphis 

 quadricornis Wedl) or by partial division into multiple lips from grooves 

 extending longitudinally over the lip {A. holoptera Rud. and A. osculata 

 Rud.). 



An interesting change occurs in the apparent tri-symmetry of the three 

 lipped cephalic structure when diminution of the dorsal sector in some 

 forms and final loss of it in others return the symmetry to bilaterality. 

 The ascarid worms belonging to the genera Polydelphis and Ophidascaris 

 possess a dorsal lip which is smaller than the ventral ones, and further 

 Ascaridia columbae Gmelin shows this peculiarity in particular. It has in 

 addition developed two very large lateral cephalic alae rising at the base 

 of the insertion of the subventral lips and extending as far as the two 

 pedunculated subsymmetrical cervical papillae. The condition of the 

 dorsal lip in such cases seems to indicate that further reduction leads to 

 complete loss of the upper pharyngeal sector or cephalic sector, according 

 to Seurat, as seen in the following genera: Protospirura, Hartertia and 

 Acuaria. Protospirura lahiodentata Hall (Fig. 31) and Protospirura ascaroi- 

 dea Hall illustrate this condition much better than Protospirura muris in 

 which the lips have been deeply cleft appearing, except for the bilateral 

 arrangement, as six separate lips, although their basal regions are partly 

 united by cuticula (Fig. 10). 



Undoubtedly a similar condition is present in the family Gnatho- 

 stomidae whose genera are characterized by two large tri-lobed lateral lips 

 with the cuticula on their inner surfaces thickened and usually raised into 

 tooth-like ridges which meet or interlock with those of the other lips. A 

 curious feature of most of the members of the family is the possession 

 of a head-bulb or cuticular swelling just behind the lips. This bulb contains 

 four submedian, subglobular, membranous structures, the so called "bal- 

 lonets," each of which is connected by one of the four cervical glands or 

 cervical sacs. The apparent function of these glands seems to be to swell 

 out the ballonets after the nematode has buried its head in the tissue and 

 in this way, with the aid of the interlocking lips, the worm assures itself of 

 a tight hold upon the host organ. The head-bulb may be coarsely striated 



