THE ROUND WORMS 47 



conspicuous. The mouth is terminal. The sexes are separate, 

 and the males are generally shorter and more slender than the 

 females. The development is usually direct (exceptions) and 

 requires no intermediate host (exceptions). 



B. Characteristics of Ascaridce. The Ascaridae are generally 

 large-sized worms (more than 2 mm. in thickness at the middle 

 in the typical Ascarids, much less in Oxyurids). The terminal 

 mouth is surrounded by three prominent papillae or lips, one 

 situated dorsally and two ventrally. The anus is located ven- 

 trally just anterior to the termination of the body. 



C. Examine specimens of Ascaris megalocephala, the round- 

 worm of the horse. This species is chosen for use because of its 

 convenient size and typical characteristics. 



a. Note sexual differences in size and the presence of two 

 terminal spicules of equal length in the male. 



b. Examine the oral papilla or lips, and the ventral trans- 

 verse anal aperture. How can you locate the dorsal and ventral 

 sides of the animal? 



c. Notice the two lateral longitudinal water-vascular canals. 



d. Measure the length of several specimens in centimeters. 

 Draw a specimen and label the parts. 



e. Examine several posterior and median cross-sections of a 

 female Ascaris, noting the presence of the intestine, and uterus 

 with ova. 



D. Examine other species of Ascaris, noting especially size 

 and color, viz. : 



a. Ascaris lumbricoides of man. 



b. Ascaris suilla of swine. 



c. Ascaris vitulorum of cattle. 



d. Ascaris mystax, the mawworm of dogs and cats. 







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