10 



BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



length). The dorsal ray split at its tip into 4 digitate processe,-', 

 the 2 external ones being the most prominent. Spicules short, 

 strongly chitinized. with thickened edges, crossing each other when 

 extruded, according to Shipley, so that the right spicule projects to 

 the left and vice versa. Gubernaculum in profile is the shape of a 

 Turkish slipper. 



Female 8 to 10 mm. long. Tail rather sharply pointed at tip. 

 Vulva (fig. 4) y 5 to y Q of body length from posterior end, the vulva 

 a transverse slit with crenelated edges. Eggs 72 to 75/t long by 46^ 

 wide, in the morula stage as passed by host. 



Life history. — According to Leiper, the embryo may develop and 

 the eggs hatch in 36 to 48 hours after the eggs leave the bird, or 

 under unfavorable conditions in summer hatching may require a 

 month. The young first-stage larva is 360^ long by 15/a wide, and 

 has an esophageal bulb and a cylindrical buccal capsule. In 4 or 5 

 days it may molt to form a second-stage larva 46G> long, which 



aosrrm 



Fics. 1-4. — 1, Trichostrongylus tenuis. Mali: bursa. X 150. After Rail- 

 liet, 1893. 2, Trichostrongylus pergracilis. Bursa ; lateral view. 

 Original. 3, Same. Dorsal and externo-dorsal rays of bursa. Original. 

 4. Same., Terminal genitalia of female. After Shipley, 1900 



slowly loses its buccal capsule. Following the next molt the re- 

 sultant third-stage larva retains its old cuticle as a sheath. This 

 larva is very resistant and has the habit of ascending vegetation in 

 the presence of moisture. When swallowed by a grouse the larva 

 apparently undergoes two more molts and becomes an adult, ap- 

 parently reaching the stage of egg production in as little as 4 days. 

 Distribution. — Europe and North America (United States 

 (Georgia) ). 



TRICHOSTRONGYLUS TENUIS (Mchlis, 1846) Railliet and Henry, 1909 



Synonyms. — Strongylus tenuis Mehlis, 1846 (in Creplin. 1846) ; 

 Strongylus serratus Linstow, 1876. 



Hosts. — Anas boschas, A. boschas dofnestlcus., Anser albifrons, A. 

 anser, A. cinereus, A. cinereus do?nesticus i A. domesticus, A. ferus, 



