THE ASCARIS 



Phylum Nematoda Class Phasmidia 



Exercise 1. — Occurrence and External Features. 



(a) Various species of Ascaris and related genera are found para- 

 sitic in the intestines of pigs, horses, man, and other vertebrates. 

 Living worms may be collected in packing houses or may be obtained 

 in smaller numbers from a freshly etherized cat or dog. Specimens 

 from the latter sources are usually small and not so desirable for study 

 as the larger species from the horse or pig. 



(b) Examine a preserved specimen of Ascaris, noting the general 

 shape of the body. What kind of symmetry is exhibited? The 

 dorsal and ventral surfaces are each marked by the narrow, white, 

 dorsal and ventral longitudinal lines; broader lateral longitudinal 

 lines are present along the sides. The mouth is at the anterior end 

 with one dorsal lip and two ventro-lateral lips. The anus will be 

 found ventrally near the posterior end. Bristle-like penial setae pro- 

 ject from the anus in the male. Mature males are smaller than the 

 females and are further marked by a bend in the body near the pos- 

 terior end. The genital pore in the female lies on the mid-ventral 

 line about one-third of the worm's length from the anterior end. :Make 

 figures (X 1) to show the general shape of both the male and the 

 female. Draw the anterior and posterior ends of each ( X 5) to show 

 the details of external features. 



Exercise 2.— General Internal Structure. 



(c) Pin a specimen out, dorsal surface up, under water in a dissect- 

 ing pan. Cut through the body wall along the dorsal mid-line, expos- 

 ing the internal organs but being careful not to injure them. Can 

 you make out the outermost layer, or non-cellular cuticle, of the 

 body wall? 



(d) The digestive system consists of a straight tube running 

 throughout the length of the body cavity, or pseudoccel. The anterior 

 end of the digestive tract is differentiated into a muscular pharynx. 

 What is its function? The major portion of the tract is non-muscular 

 and consists only of endoderm, bounded internally and externally by 

 a thin, non-cellular cuticle. The posterior portion of the tract is 



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