PISCES. 167 



The spermaries (testes) are two soft flattened bodies, each 

 connected by a number of small ducts (vasa efferentia) with the 

 front end of the corresponding mesonephros. 



The kidney is made up of numerous glandular tubules, and 

 the sperms have to traverse some of these before they can reach 

 the urino-genital duct. 



The urino-genital sinus is forwardly produced into two blindly- 

 ending sperm sacs situated on the ventral side of the kidneys. 



The daspers serve as copulatory organs by which the sperms 

 are introduced into the oviducts of the female. 



Two short tubes, with a common opening into the abdominal cavity, can 

 be seen on the ventral side of the gullet. These are rudimentary Mullerian 

 ducts, equivalent to the oviducts of female specimens. 



The kidneys in the female exhibit the same regions as in the 

 male, but the mesonephros is not so well developed. The two 

 mesonephric ducts are straight and unite to form a urinary sinus, 

 which receives a number of distinct metanephric ducts and opens 

 into the cloaca on a dorsal urinary papilla. 



The reproductive organs of the female are not so intimately 

 connected with the urinary organs as in the male. There is a 

 large unpaired ovary from which large ova in various stages of 

 development can be seen projecting. When ripe these may 

 exceed half an inch in diameter, their large size being due to 

 the presence of abundant food-yolk. 



The oviducts (Mullerian ducts) have a common anterior open- 

 ing into the abdominal cavity, situated on the ventral side of the 

 gullet in front of the liver. Each of them curves back and soon 

 dilates into an ovoid oviducal gland, after which it runs back as a 

 good-sized tube towards the cloaca, just before reaching which it 

 unites with its fellow to open by a median dorsal aperture. 



The ova are fertilized in the oviduct, after which each of them 

 is surrounded by an albuminous fluid and enclosed in a horny 

 case secreted by the oviducal gland, and with four corners pro- 

 duced into tendril-like threads. In this condition the eggs are 

 laid, the threads serving to attach them to seaweeds, &c. De- 

 velopment takes place at the expense of the food-yolk, which 

 after a time is found stored in a vascular sac, the yolk-sac, 

 attached to the ventral side of the embryo. 



In most dogfishes the entire embryonic development takes place in the 

 oviduct, and in one species (Mustelus Ia3vis) the vascular yolk-sac is thrown 



