GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 11 



Other than G. nasalis, which sometimes attaches in the pharynx, 

 the first-stage larvae attach to various portions of the stomach and 

 duodenum. In the stomach young larvae have been removed from 

 various locations, including both the cardiac and pyloric portions. 

 The last-stage larvae of all three species are found in the various por- 

 tions. Gasti'ophilus intestinalis is confined for the most part to the 

 mucosa of the left sac, though this species has been taken in the 

 right sac and in the duodenum (see Table I). In the early stages 

 some of the larvae either change places of attachment or pass out of 

 the horse undeveloped. With last-stage larvae the indications are 

 that, excepting G. haemorrhoidalis, they remain attached at one 

 place continuously during feeding, as in early spring the number of 

 larvae and lesions upon the mucosa is the same. 



During the early spring or perhaps even in winter the larvae of 

 G. haemorrhoidalis move from the stomach and duodenum to the 

 rectum where they may be found permanently attached in clusters. 

 It is evident that they feed in this position, as lesions are sometimes 

 present. Later when they move to the margin of the anus no lesions 

 are present and apparently the larvae only pause to become accustomed 

 to air temperatures before dropping. 



There is no definitely periodic larval migration of G. haemorrkoi- 

 dalis, as some last-stage larvae are found in the stomach and duode- 

 num until early fall. Through the courtesy of Dr. L. Van Es, of the 

 North Dakota Experiment Station, some post-mortem examinations 

 were made at Fargo, N. Dak., and larvae preserved according to 

 their location within the animal. During the winter these larvae 

 were found in the stomach, and on July 10, 1916, 3 larvae; July 14, 

 1916, 16 larvae; and August 18, 1916, 2 larvae Were fully developed 

 and in the same regions. This coincides with the findings at Aber- 

 deen, S. Dak., although one last-stage larva was found in the stomach 

 on September 8, 1916. 



POINTS OF LARVAL ATTACHMENT. 



When an opened stomach of a horse is examined, one is impressed 

 by the contrast in the left and right portions. Around the entire 

 organ a line of demarcation is represented by a prominent sinuous 

 crest. In the left portion, which is often called the left sac, the 

 mucosa is white, dry, resistant, and covered by a thick layer of 

 epithelium. This covering is identical with that of the esophagus 

 and may be considered as a widening of the esophageal canal. 



Dr. Guyot, in describing the mucosa of the left sac, says the struc- 

 ture is analogous to that of the skin. It is dermo-papillary, with 

 epithelium of the Malpighian type, but possesses a muscle, the 

 mmcularis mucosae, which is peculiar to it. The structure of the 



