REPRODUCTION 



207 



In all flukes except those of the family Schistosomidse both 

 male and female reproductive systems occur in the same individ- 

 ual, and occupy a large portion of the body of the animal. We 

 are familiar with animals which appear to live almost wholly 

 to eat; the flukes are animals 



which seem to live merely for re- J^^i " "*' 



production. They are reproduc- £M\^^ '''' 



tive machines, all the other or- /f'/^V^'i'-t o nat.»u, 



gans of their bodies being devel- f'U/jmMy^ >"» 



oped only to a sufficient extent ri/7^^%4 v.s. 



to ensure the proper develop- l-mSPw^l — ■'■'' 

 ment and maturity of the eggs. p^^^^^^sk"" ^^ ^ 



The eggs proper and the shell f^im^^^ a i mm --"*' 

 materials are produced by sepa- ls^^^^™K"- °*- 

 rate glands, and sometimes the vi^^^^ffil^|^--^^.r. 

 canal for conducting the sperms 'S^P^^^®'^- - -- 1 



from another individual into the ^^^jtS^" -ext.c. 



body to fertilize the egg is distinct 



r ii. J. I.- 1. J J. J.1 Fig. 62. Heterophyes heterophyes, a 



from that which conducts the ^ery small intestinal fluke of man; A, 



eggs out of the body. The male adult; B ( X 350), spines from genital 



, ■ i r X ring; g. r., genital ring; g. p., genital 



system consists of two or more pores; other abbrev. as in Fig. 74. X 33. 



glands or testes for the produc- Egg shown above, x 500. (After 

 tion of the sperms, two sperm 



ducts which meet and enlarge into a "cirrus pouch" for storing 

 the sperms until ready to be used, and a rectractile copulatory 

 organ. All these complex sexual organs in a single animal which 

 may be no larger than the head of a pin (Fig. 62)! 



Almost as soon as the fluke reaches its final host and assumes 

 its mature form, development of the reproductive systems be- 

 gins. Although both sexes are usually in the same individual, 

 mutual cross-fertilization generally takes place, the sperms of 

 two individuals simultaneously fertilizing each other. The num- 

 ber of eggs maturing in a single fluke is enormous, and while it 

 undoubtedly varies in different species and in different individuals, 

 the £ggs are probably always to be reckoned in the thousands, 

 and sometimes in the hundreds of thousands. 



Life History. — The life histories of all the flukes which are 

 internal parasites have much in common, and all of them undergo 

 a series of marvelous transformations from egg to adult. 



The fluke which is most thoroughly known in every respect 



