20D DISPERSAL OF PARASITIC EGGS 



to a certain extent without breaking. In this way a globular 

 egg can be pressed into an ovoid shape. This is of importance 

 in relation to the ingestion of eggs by flies. 



"The general surface of the shell may be either smooth or 

 slightly roughened. It is usually covered by a layer of mucus 

 when it is being extruded by the worm, and it may receive an 

 additional coating of mucus in the intestine of the host. This 

 imparts to it a certain degree of adhesiveness. In some cases 

 the eggs are laid in batches surrounded b)' a gelatinous or 

 mucous investment. 



" The size of the eggs varies in different worms. The\' are 

 rarel}' smaller than "Oi mm. or larger than "15 mm. in length. 

 The breadth is most commonly half to two-thirds the length. 

 Even in the same worm the eggs , vary considerably in size 

 although they usually approximate towards a definite size and 

 shape, which is more or less characteristic for the species. On 

 that account the eggs of most species of human parasites can be 

 recognized very readily. In the following list the parasites of 

 man are arranged according to the size of their ova, the sizes 

 given being approximate averages. They are divided into three 

 sections, the first of which contains those whose eggs do not 

 exceed "045 mm. in both diameters, the second comprises those 

 with eggs of which the breadth is less than "045 mm., while in 

 •the third the minimum diameter exceeds '045 mm. The reason 

 for this division is, as will appear later, that Musca donicstica is 

 apparently unable to ingest particles of larger size than about 

 •045 mm. 



I. Opisthorcis felineus ... 

 Clonorchis sinensis ... 

 Heterophyes heterophyes , 

 Opisthorcis noverca... 

 Oxyuris vermicularis 

 Taenia saginata 

 Trichuris trichiurus ... 

 Tc-enia solium 

 Taenia echinococcus 

 Dicroccelium lanceatum 



