REPRODUCTIVE ORGANS 



403 



former, or " gymnoarian," condition is primitive ; the latter, or 

 " cystoarian," is secondary, and is brought about by the growth 

 of two peritoneal folds round the ovary and the union of their 

 margins. Into these coelomic sacs the egg-bearing or real ovarian 

 tissue projects either in the form of processes or of trans- 

 versely- or longitudinally -arranged plates or folds (Fig. 232, B). 

 The testes are composed of seminal ampullae, as in Elasmo- 

 branchs, or of radially-arranged and sometimes plexiform tubules 



FIG. 232. Diagrams to show tl.ie structure of the testes (A) and of the ovaries (B) 

 in a Herring. (From Cunningham.) 



opening into the gonoduct, as in nearly all other Fishes (Fig. 

 232, A). 



In the Cyclostomes (e.g. Petromyzon} the eggs and sperma- 

 tozoa are discharged from the gonads into the coelom, whence 

 they reach the exterior through a pair of " genital pores " leading 

 from the hinder end of the coelom into a urinogenital sinus 

 formed by the united extremities of the two archinephric ducts. 1 

 Myxine has, however, but a single median pore, opening into an 

 integumentary cloaca, which also receives the rectal and urinary 

 orifices. Bdellostoma has two such pores communicating with 

 *i similar cloaca. 2 



1 Ewart, Journ. Anat. and Phys. x. 1876, p. 488. 



2 Burne, Linn. Soc. Journ. Zool. xxvi. 1898, p. 487. 



