670 



NEMA THELMINT HES 



latter many are killed in the lymphatic glands, but some get through 

 to the blood, and in this way are carried to the lungs. They now 

 work their way out of the capillaries into the lumen of the air cells, and 

 travel up the bronchi, trachea, and larynx into the oesophagus (they 

 might by chance get into the mouth), and so through the stomach to 



Fig. 295. — Aucylostoma duodenale Dubini: Development of the 

 Rhabditiform Embryo. 

 (After Looss, except the last figure, which is after Perroncito.) 



the intestine. The time occupied by this journey is believed to be 

 from seven to ten days. In the skin they undergo their second 

 ecdysis, and later a third and fourth ecdysis takes place in the alimen- 

 tary canal, the third in four to five days and the fourth from four to 

 six days after their arrival. They now measure 3 to 5 millimetres in 



length, and eight days later 

 the generative organs begin 

 to attain maturity, and the 

 first copulations take place, 

 and a few days later the first 

 eggs appear in the faeces, thus 

 completing the cycle of de- 

 velopment, of which the por- 

 tion after infection occupies 

 four to six weeks. 



The more important morpho- 

 logical changes which take place 

 in the human body may be briefly 

 recapitulated. 



On entering the skin the third 

 stage of development begins, 

 during which the provisional 

 buccal capsule is formed. A 

 third ecdysis ushers in the fourth 

 stage, characterized by the pro- 

 visional buccal capsule armed 

 with a dorsal and a ventral pair 

 of teeth. During this stage the sexes become differentiated and the permanent 

 buccal capsule is formed. The fourth ecdysis results in the appearance of 

 the adult worms. 



The number of females can be calculated from the number of 



eggs in the faeces by the formula Z= — , where X is the number 



47 



offemales and A the number of eggs in a gramme of faeces. 



Fig. 296. — Hatching of Egg of Ancylo- 

 stoma duodenale Dubini, 1843. 



(From a photograph by J. J. Bell.) 



