112 



PRACTICAL PARASITOLOGY 



the eggs of Ankylostoma duodenale are oval and thin-shelled, and are 

 deposited, either before the germinal groove appears, or while it is still 

 in a very early stage of development. The eggs of Oxyuris vermicularis, 

 on the other hand, though oval, are furnished with a thick shell and 



contain an embryo resembling a tad- 

 pole (fig. 39). This embryo, when 

 subjected to sufficient heat, passes 

 in the course of a few hours into 

 a nematoid stage of development. 

 The degree of difference which may 

 subsist between closely allied species, 

 is shown by a comparison of the 

 eggs of A. lumbricoides with those 

 of A. canis (= A. mystax) (fig 40). 

 Unfertilized eggs of Ascarides 

 are frequently found in the stools of 

 man. These differ from normal 

 eggs ; firstly, in their shape, which 

 is longer; secondly, in their con- 

 tents, which are richer in yolk- 

 granules"; and thirdly, in the manner 

 in which the germinal cell entirely 

 fills the shell. Eustrognylus gigas 

 (fig. 41) is distinguished by the 

 peculiar thickness of its shell, which, 

 except at the poles, is of a brownish 

 colour and is very much pitted. The 

 eggs of Trichocephalus are also oval, 

 but they are flattened at the poles 





FIG. 36. Dipylidium caninum (L.). 

 Left, scolex ; right, at the top, a bundle 

 of eggs ; underneath it, hooks from the 

 rostellum, seen from the front and in 

 profile ; at the bottom, an egg. (After 

 Diamare.) 



FIG. 37. Egg of 

 Dibothriocephalus latus 

 (L.). 240:1. 



FIG. 38. Eggs of Ankylostoma duodenale in different 

 stages of development, a c, In fresh faeces. 336: 1. 



and appear barrel-shaped. The shell is thick, brownish in colour, and 

 perforated at the poles, the openings being closed with a light mass. 

 These eggs are deposited before the developmental changes commence, 

 the shell, in this case also, being entirely filled by the granulated 

 germ-cell (fig. 42). 



