DISPERSAL OF PARASITIC EGGS 



20 1 



H}M'nenolepis nana ... 

 Dip}-Hdium caninum 

 Davainea madagascarensis 



II. Ank)'lostoma duodenale 

 Ternidens diminutus 

 Necator americanus 

 Trichostrongylus subtilis 

 Schistosomum japonicum 

 Ascaris lumbricoides 

 Eustrongylus gigas ... 

 Dibothriocephalus latus 

 Schistosomum haematobium 



III. Diplogonoporus grandis 



Dibothriocephalus cordatus 

 Hymenolepis diminuta 

 Paragonimus vvestermanni 

 Belascaris mystax ... 

 Toxascaris h'mbata ... 

 GastrocHscus hominis 

 Fasciolopsis buski . . . 

 Fasciola hepatica 



" The resistance of eggs to external conditions is also of im- 

 portance. All do not withstand similar conditions equall)- well. 

 For many, moisture is absolutely essential, and in its absence 

 they rapidly die. This is true for the eggs of practically all 

 Trematode worms. Many of these can survive only in sea 

 water, others only in fresh water, and changes in the composition 

 of the water affect them injuriously. Drying is usually fatal 

 within a few hours ; the shell becomes crumpled and shrivelled 

 up, the embryo dies and the subsequent application of moisture 

 does not resuscitate it. On the other hand, eggs of some tape- 

 worms and round-worms can survive desiccation for comparatively 

 lengthy periods. For instance, I have kept the eggs of Hymeno- 

 lepis diminuta in dry powdered faeces for as long as 17 days, at 

 the end of which time man}' of them were still alive. In the 



