541 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



the vulva is a long, narrow transverse slit, sometimes slightly salient. 

 There are a very short vagina and two divergent ovejectors. Eggs 

 are elliptical, comparatively thin-shelled, and segmenting when 

 deposited. 



The only known species occurs in the stomach of swine. 



Type species. — Strongylus rubidus Hassall and Stiles, 1892. This 

 worm is designated as Hyostrongylus rubidus (Hassall and Stiles, 1892) 

 Hall, 1921. Travassos, in an undated reprint which has just come 

 to hand, puts S. rubidus in the genus Ostertagia, but this species 

 lacks the accessory bursal membrane characteristic of species of 

 Ostertagia. 



The type species, Hyostrongylus rubidus, has already been described 

 by Hassall and Stiles (1892) in their original report on this worm, but 

 the following point should be noted in regard to this species: In 

 their original description, Hassall and Stiles figure the lateral portions 

 of the telamon as filamentous. This is due to the fact that this 

 structure is colorless and highly transparent, very difficult to find or 

 study in alcoholic or mounted material, and they have drawn the 

 outline and overlooked the included structure. It has been found 

 advantageous in studying this structure to resort to staining with 

 gentian violet. This is a very rapid, penetrating, and amenable 

 stain, which can be used in water or any strength of alcohol, the 

 specimens being subsequently mounted in glycerine jelly or in balsam. 

 It clears rapidly and shows a tendency to decolorize, so it is perhaps 

 better suited for staining material for immediate study than for per- 

 manent mounts. It stains the rays of the bursa and many of the 

 internal organs very well, and also stains the accessory supporting 

 structure which is designated as the telamon in such forms as Hyo- 

 strongylus rubidus. The so-called chitinous structures, such as the 

 spicules, which are brown, do not take the stain, as a rule. Staining 

 develops the fact that there is a transparent structure which connects 

 the posterior end of the gubernaculum proper to the irregularly oval 

 or quadrangular structure, which Hassall and Stiles regarded as the 

 cloacal aperture, showing that these are parts of one structure. The 

 quadrangular structure is too small to permit the passage of the spic- 

 ules, even if it represented a true aperture. It is situated on the 

 conical tip of the body, inside of the bursal cavity, and gives the tip 

 of the body an appearance of being bifid or bicornate in profile when 

 seen in some views. The cloacal aperture is ventral of this conical 

 body termination and is very vague in outline, even in stained prepa- 

 rations. 



The gubernaculum and telamon appear to be modifications of the 

 cloacal wall, either by local thickening and condensation or by the 

 deposition of material of suitable hardness for the protection of the 

 cloacal walls from] the passage ofj[the sharp, pointed spicules, and for 



