382 Animal Biology 



Reproduction. — The sexes are in separate animals; hence, they are 

 diecious (di -e' si us) (Gr. di, two; oikos, house). The m,ale reproduc- 

 tive organs include one coiled, threadlike testis which leads into a tubular 

 vas deferens. The latter joins a wider seminal vesicle which connects 

 with a muscular ejaculatory duct, opening into the rectum. One pair of 

 spicules, called penial setae, protrude from the anus and assist in trans- 

 ferring sperm to the female during copulation. 



The female reproductive organs include one pair of coiled, threadlike 

 ovaries, each connected with a larger uterus. The two uteri unite to 

 form a short, muscular vagina (va-ji'na) (L. vagina, sheath). The 

 latter empties through the genital pore about one- third the length of the 

 body from the anterior end. 



Fertilization occurs in the uteri and each egg is then enclosed by a 

 shell of chitin (ki' tin) (Gr. chiton, tunic or covering), after which it 

 passes from the genital pore. One female may possess more than 

 25,000,000 eggs, and a mature female may lay 200,000 daily. They are 

 laid inside the host intestine and pass with the feces. The eggs are re- 

 sistant and may remain alive in the soil for months. When eggs which 

 contain embryos are ingested through the mouth, infestation may result. 

 The ingested eggs hatch in the intestine, where the embryonic larvae 

 bore through the intestinal wall into the lymphatic vessels or capillaries. 

 They eventually enter the right side of the heart, from which they pass 

 in successive stages to the lungs, trachea, esophagus, stomach, and in- 

 testine. This entire journey requires a little more than a week. 



QUESTIONS AND TOPICS 



1. List all the ways in which Platyhelminthes and Nemathelminthes differ. 



2. List the characteristics which planaria, the tapeworm, and the liver fluke 

 have in common. 



3. Make a table of the animals studied, including all the ways in which they 

 differ. 



4. Describe each of the following for each animal studied: (1) integument, 

 (2) motion and locomotion, (3) ingestion and digestion, (4) circulation, 

 (5) respiration, (6) excretion and egestion, (7) coordination and sensory 

 equipment, and (8) reproduction. 



5. Discuss the significance of ( 1 ) bilateral symmetry, (2) triploblastic, (3) sexual 

 dimorphism, and (4) hermaphroditism. 



6. Discuss specifically what effects prolonged parasitism seems to have had on 

 such systems as the digestive, circulatory, and sensory of the parasite. 



7. Discuss the phenomenon of axiate organization and its significance. 



8. Discuss specifically the structures and abilities which certain parasitic worms 

 possess whereby they are able to live successfully in spite of many obstacles. 

 Explain how the production of large numbers of offspring enters into this 

 consideration. 



