258 



HOOKWORMS 



Fig. 104. Eggs of hookworms in early stages 

 of segmentation, — four-segmented type most 

 common in faeces; A, Necator americanus ; B, 

 Ancylostoma duodenale. 



the host, usually in a continuous stream, but occasionally with 

 intermissions, to be passed with the faeces. The thin-shelled 

 eggs, which are about 60 ^ by 35 ai {-^is by 7^^ of an inch) in size, 

 and slightly larger in the American species, undergo the first 

 stages of development while still in the intestinal canal, and by 

 the time they are voided with the faeces they are segmented into 



from two to eight cells 

 (Fig. 104). The segmented 

 condition, together with 

 the fact that they are clear 

 and not yellow or brown 

 from bile stain, distin- 

 guishes the eggs from those 

 of many other worms 

 found in the intestine. 

 Further development does 

 not take place until the 

 faeces are exposed to air, 

 when, if moisture is present and the temperature is moderately high 

 (65° to 85° F.), the development continues and the embryo hatches 

 in from 24 to 48 hours (Fig. 103C). Below 65° F. development is 

 very slow, and above 85° F., although development is very rapid, 

 the eggs and larvae are likely to die. The newly hatched worm is 

 about 0.2 mm. (less than a hundredth of an inch) in length with a 

 bottle-shaped oesophagus, a simple intestine, and practically no re- 

 productive organs. The most favorable conditions for the devel- 

 opment of the larvae, in addition to the temperatures mentioned, 

 are a moderate degree of moisture, presence of air, plenty of food 

 in the form of decomposing organic matter, and not too rapid 

 putrefaction. According to Looss, the larvae will not develop 

 well in faeces derived from a purely vegetable diet, a small propor- 

 tion of animal matter being essential for food. Enough animal 

 food for some development would always be provided by blood 

 from intestinal hemorrhages. On the other hand a purely meat 

 diet is unfavorable on account of the rapid putrefaction. If 

 suitable conditions are present, the larva grows rapidly for four 

 or five days, shedding its skin at the end of the second day. In 

 about five days, under ideal conditions, the skin begins to be- 

 come detached again but is not shed. It is retained as a flexible 

 protecting sheath for the larva, but does not hinder free motion 



