LIFE History of ascaris lumbricoides. 



19 



jmterior end of body 0.12 mm., distance of anus from tip of tail 

 0.08 mm., and distance of genital primordium from tip of tail 0.48 

 mm. The 

 body is of 

 nearly 

 u n i form 

 diamet&r 

 through- 

 out, attenuated slightly from the base of the esophagus 

 forward, and gradually from the beginning of the 

 posterior third of the body backward, diminishing to 

 about half its maximum diameter in the anal region; 

 tail conical. Along each lateral line is a well-marked 

 membrane (shown in cross section in figure 6). Th-e 

 mouth is small, pharynx very short, the esophagus 

 beginning almost immediately back of the mouth ; lips 

 not conspicuous, the knoblike process on the anterior 

 aspect of the head characterizing 

 the newly hatched larva being no 

 longer present. Just in front of 

 the bulbous posterior end of the 

 esophagus, sometimes on the 

 right side, sometimes on the left 

 side, is the large nucleus of a 

 cervical gland. The genital pri- 

 mordium is small, not more than 

 0.015 mm. in diameter, oval in 

 shape, consisting of a very few 

 cells, situated on the ventral side 

 of the intestine some distance 

 posterior of the middle of the 

 body. 



In the living worm the eso- 

 phageal region is clear and trans- 

 parent, the intestinal region jel- 

 lowish-brown through the pres- 

 ence of numerous granules of 

 this color in the intestinal cells 

 (figure 4), 



Fig. 3. — Ascaris suum. Larva from lung of 

 rabbit 10 days after infection. Slightly 

 flattened by pressure of cover glass. 

 Magnified 150 times. 



RELATION OF HOST TO SIZE OF DEVELOPING LARVJE. 



Parasites that are able to live in more than one species of host 

 animal frequently exhibit differences of size in different species of 

 animals. A good example is the gapeworm {Syngamus trachealis), 



