ASCARID^E 



167 



children, whilst in the Tropics it occurs at all ages and 

 sometimes in enormous numbers. This well-known 

 worm varies in colour, but is usually grey or partly 

 reddish. 



Though the worms may be passed per os or per rectum 

 the diagnosis is usually made by examination of the stool 

 for ova. The ova vary greatly in appearance as they are 

 seen in the stools. This variation depends in part on an 

 albuminous covering which varies in thickness. The 

 colour is brownish-yellow, as it is stained by the colour- 

 ing matter in the faeces. The contents of the egg vary, 

 as some eggs are not fecundated. 



FIG. 66. Ascaris lumbricoides. a, posterior extremity of the male with 

 the spicules protruding from the orifice of the cloaca (Sp. ) ; b, anterior 

 extremity from the dorsal surface ; c, anterior extremity from the ventral 

 surface ; P., porus excretorius. (From Glaus.) 



The egg varies in shape ; it is usually elliptical but some- 

 times nearly spherical. It is composed of a thick trans- 

 parent shell which is not stained by the faeces and encloses 

 the unsegmented ovum which does not completely fill 

 the shell. When the egg is not fecundated the contents 

 contain numerous refractile globules, probably un- 

 absorbed food material, and may then appear to be 

 composed of numerous unequal segments. 



In the great majority of cases the egg-shell is covered 

 with an albuminous coating which is rough and irregular 

 on its outer surface and brownish in colour. It may be 

 absent or in some cases easily detached. In the prepara- 

 tion for microscopic examination the albuminous coating 

 is often detached in part or altogether, especially if the 



