34 GUIDE TO THE STUDY 



lumbricoides serves admirably, being large enough for easy 

 dissection and presenting no complicated or highly specialized 

 arrangement of organs. 



Ascaris lumbricoides belongs to the superfamily Ascaroidea. 

 In the course of the following study, the student should carefully 

 check over the characteristics of this group, as given by Yorke 

 and Maplestone: "Eunematoda; usually fairly large and stout; 

 head bilobed; oesophagus frequently more or less enlarged pos- 

 teriorly, but without a definite spherical posterior bulb containing 

 a valvular apparatus (except in Dujardinia, where there is a 

 small, unarmed bulb), with or without diverticula. Spicules 

 equal or unequal. Females not much larger than the males." 



PRACTICAL WORK 



External Features. — Note the general form of the body, which 

 in the Ascaridse is relatively thick. The mouth is surrounded by 

 three lips, one dorsal and two ventro-lateral. Running length- 

 wise of the body are four equidistant lines, a dorsal, a ventral, and 

 two lateral lines. About two millimeters from the anterior end is 

 the minute excretory pore in the median ventral line. 



Dissection. — The female worm may be distinguished from the 

 male by her greater size and gently curving caudal end. In the 

 male the caudal end is sharply curved to form a hook, and two 

 spicules may be seen at the anal opening. In the female the 

 genital opening is also ventral and situated about one-third the 

 length of the worm from the anterior end. The mouth opens 

 between the three lips at the anterior end. The anal opening is 

 at the caudal end. 



Make an enlarged drawing of the ventral anterior end of the 

 body showing the lateral lips and the position of the excretory 

 pore. Make an outline drawing of the entire worm showing the 

 position of the mouth, anus, excretory pore, genital opening, and 

 lateral line. 



Slit a female worm very carefully longitudinally just laterad of 

 the median dorsal line and pin out the body in a dissecting pan. 

 To prevent the specimen from drying, cover it with ^ inch of 

 water. Note the alimentary canal consisting of a straight tube 

 running from mouth to anus. Three sections may be distin- 

 guished : a short oesophagus, the long flattened mid-intestine, and a 

 short rectum. The lateral line can be seen as an inward projecting 

 ridge separating the longitudinal muscles. Locate the genital 



