CHAPTER IX 



THE ORGANS OF REPRODUCTION 



JIHE Germ-cells. — In most fishes the germ-cells are pro- 

 duced in large sacs, ovaries or testes, arranged sym- 

 metrically one on either side of the posterior part of 

 the abdominal cavity. The sexes are generally but not always 

 similar externally, and may be distinguished on dissection by 

 the difference between the sperm-cells and the ova. The ovary 



Fig. 91. — Sword-tail Minnow, nnale, X iphophorus helleri Heckel. 

 modified as an intromittent organ. VeTa Cruz. 



The anal fin 



with its eggs is more yellow in color and the contained cells 

 appear granular. The testes are whitish or pinkish, their secre- 

 tion milk-like, and to the naked eye not granular. 



In a very few cases both organs have been found in the 

 same fish, as in Scrranus, which is sometimes truly hermaphrodite. 

 All fishes, however, seem to be normally dioecious, the two sexes 

 in different individuals. Usually there are no external genital 

 organs, but in some species a papilla or tube is developed at the 

 end of the urogenital sinus. This may exist in the breeding 

 season only, as in the fresh-water lampreys, or it may persist 

 through life as in some gobies. In the Elasmobranchs, carti- 

 laginous claspers, attached to the ventral fins in the male, serve 

 as a conduit for the sperm-cells. 



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