NEMATODE PARASITES 



201 



Apart from the general features characteristic of a small nematode 

 the most striking characteristics are two. (i) The mouth opening (Fig. 

 92, A) has become shifted on to the dorsal surface of the head, and there 

 project into its cavity upon each side two strong recurved spines. A 

 little further back there projects upwards from the floor of the cavity 

 a pair of flat cutting blades. (2) In the male (Fig. 93) the edges of the 

 anal opening project into a conspicuous thin flap on each side which 

 serve to grip between them the body of the female. 



The mature worms are to be found especially in the small intestine, 

 holding on by their hooks and feeding on 

 the lining epithelium and the underlying 

 connective tissue with its capillaries. 



The eggs (Fig. 90, C), ellipsoidal in shape 

 and enclosed in a delicate shell measuring 

 about 60 //, x 37 //,, are laid in the intestine 

 and pass to the exterior amongst the faeces. 

 If conditions are favourable the ground 

 being moist and the temperature warm 

 ( 2 5"35 C.) the egg hatches out within n 

 couple of days as a small larva about a 

 quarter of a millimetre in length. These 

 larvae have pointed tails and show certain 

 resemblances to another genus Rhabditis 

 from which fact they are often spoken of as 

 the Rhabditis-stage. The larva feeds actively 

 on faecal matter, grows to about double its 

 original length, and casts off the outer 

 layer of its cuticle. This process of moult- 

 ing is repeated but this time the shed 

 cuticle remains as a loose membranous 

 sheath round the body of the worm. The 

 worm now a week to ten days old has lost the Rhabditis character- 

 istics ; it ceases to feed and becomes sluggish in its movements but is 

 capable of remaining alive for several months so long as it is kept wet. 

 It is this stage, after the second moult, that is alone capable of infecting a 

 new mammalian host. 



This may take place through the worm simply being swallowed, for 

 example in drinking water or among insufficiently cleaned vegetables. But 

 Looss discovered by a personal accident that the Ancylostoma may find its 

 way to its destination by a much more circuitous route. While carrying 

 on investigations in his laboratory in Cairo he let fall on his hand a 



FIG. 92. 



Enlarged view of dorsal side of 

 head end of A, Ancylostoma and B, 

 Necator, to show the buccal cavity. 



