36 BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



filled with eggs, the uterine coils extending almost to posterior end 

 of body (x in fig. 36). The conical tail end bears a pointed process. 

 The prominent vulva in immature worms is about one-fourth, in 

 gravid worms about one-sixth, of the body length from the anterior 

 end. The ellipsoidal eggs are operculated and 85 to 90/a long by 5(V 

 wide, or, according to Ortlepp, 78 to 100^ long by 43 to 46/*, wide. 



Embryo 280/* long; anterior end blunt, tail elongate conical and 

 pointed. The embryo in the shell may be the first or second stage 

 larva. The description applied to the second stage larva. 



Larva, third stage, in lungs, of 2 types. Male with obliquely trun- 

 cated tail and up to 1.16 mm. long. Female with pointed tail and 

 up to 1.42 mm. long. Simple buccal capsule 9/t deep. 



Larva, fourth stage, separate or 

 copulating. Male up to 1.44 mm. 

 long. Female up to 1.98 mm. 

 long. Most of adult characters 

 present. 



Life history. — As the fully formed 

 eggs develop, they pass out of the 

 ~^r- vulva under the margin of the male 



figs. 38-39.— syngamus trachea. 38. bursa and get to the lumen of the 

 spicules. 30, male bursa. After trachea and bronchi. These eggs, 



Chapin, 1925 ... ,. , -, 5; t 



which are segmenting when deposited, 

 up to the 16-cell stage, are coughed up and swallowed, passing out 

 in the droppings. In the external world they develop infective 

 larvae under favorable conditions, as in well aerated water, in 

 about a week, and hatch in about 2 weeks (some writers say 1 

 week) or longer if conditions are less favorable. Eggs hatch at 

 25° C, according to Ortlepp, but not at 20° C. The first molt may 

 take place in the shell or after hatching, and the larvae appear to 

 be infective as second-stage larvae. These larvae sometimes lose 

 their sheaths after hatching. The fact that birds swallow a large 

 amount of mineral matter, to furnish sand, gravel and small peb- 

 bles for the gizzard, ensures their ingesting the eggs containing lar- 

 vae or the larval worms present in soil, and it is not necessary to 

 assume that the larvae are ingested on vegetation or in food or 

 water, though this too may happen. When infective larvae are 

 swallowed, they make their way to the lungs where they have been 

 found by Ortlepp 24 hours after feeding eggs. Within a week they 

 are found there as young worms not yet paired. The third larval 

 stage is reached during the third day of parasitic life, and the fourth 

 stage on the fourth or fifth day. After pairing in the lungs while 

 still fourth-stage larvae, the young worms leave the smaller air 

 passages, gradually working their way to the larger air passages 



