THE DOGFISH n 



not carry urine. At its anterior end it is connected by means 

 of delicate tubes, called the vasa efferentia, with the anterior end 

 of the testis, from which it receives sperm. The posterior por- 

 tion is not convoluted, and its hinder end is enlarged to form 

 a seminal vesicle. Through this portion the sperm is brought 

 from the epididymis to the cloaca; it also acts as a ureter, a 

 number of urinary tubes arising from the kidney and proceed- 

 ing to its hinder end. The Wolffian duct thus acts both as a 

 vas deferens, or sperm duct, and as a ureter, and on account of 

 this double function is also called the duct of Leydig. 



In the female animal the Wolffian duct is exclusively a ureter, 

 corresponding to the hinder part only of the same duct in the male, 

 and receives a number of urinary tubes from different parts of the 

 kidney. The two Wolffian ducts meet at their hinder ends, and 

 the median vessel thus formed opens into the cloaca at the end of 

 the urinary papilla, behind the rectum. 



The excurrent canals of the genital organs in the female are 

 called the Miillerian ducts, or oviducts ; they are not present in the 

 male, except sometimes as rudiments. They are a pair of large 

 tubes which extend the entire length of the abdominal cavity. 

 Their anterior ends are joined, and open into the abdominal 

 cavity by a large median pore which is situated just in front 

 of the liver and beneath the oesophagus. In the anterior part 

 of each oviduct is the large, ovoid shell gland; in its posterior 

 part is the wide, distended uterus. 



The ova are thrown into the abdominal cavity by the rupture 

 of the walls of the ovaries. They pass into the oviducts through 

 the median pore just mentioned, where they are fertilized. They 

 remain in the uterus, while development takes place, the young ani- 

 mals being born alive ; in many oviparous sharks a characteristic 

 black, horny shell is formed in the uterus. 



Exercise 11. Make a semidiagrammatic drawing of the urogenital 

 system, so far as observed, together with the cloaca. 



The Nervous System. This is made up of three groups of 

 organs: (i) the central nervous system, which includes the brain 

 and the spinal cord; (2) the peripheral nervous system, which 



