STRUCTURE OF THE LEECH. 



219 



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The Excretory System. 



The excretory system includes seventeen pairs of excretory 

 tubules or nephridia, opening laterally 

 on the ventral surface, ending blindly 

 within the body, but extracting waste 

 products from the blood vessels which 

 cover their walls. Each consists of two 

 parts, a twisted horse shoe shaped 

 glandular region where the actual ex- 

 cretory function is discharged, and a 

 spherical, internally ciliated bladder 

 opening to the exterior. Within the 

 latter there is a whitish fluid in which 

 microscopic examination shows numer- 

 ous waste crystals. The nephridia 

 secrete a clear fluid which helps to 

 keep the skin moist, and thus makes 

 respiratory diffusion easier. 



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The Reproductive System. 



The leech, like many other Inverte- 

 brates, is hermaphrodite, containing 

 both male and female reproductive 

 organs. The essential male organs or 

 testes are diffuse, being represented by 

 nine pairs, lying on each side of the 

 nerve cord in the middle region of the 

 body. Each is a firm globular body, 

 within which mother sperm cells divide 

 into balls of sperms. The spermatozoa 

 pass from each testis by a short canal 

 leading into a wavy longitudinal vas 

 deferens. This duct followed towards 

 the head forms a coil (so-called seminal 

 vesicle) as it approaches the ejaculatory 

 organ or penis. From the coil on each 

 side the sperms pass into a swollen sac 

 at the base of the penis, where by the 

 viscid secretion of special (" prostate ") glands, they are glued 

 together into packets or spermatophores. These pass up 



Fic. 71. — Dissection 

 of Leech. 



rg.., Nerve ring around 

 cesophngus, here incom- 

 plete; /., peni.s ; ^.7'., 

 seminal vesicle ; m'., 

 ovary ; nt.. uterus ; ZKd.. 

 vas deferens ; /., one of 

 the testes: «., nephridium 

 with bladder (/'/.) ; i'., a 

 ganglion on ventral nerve 

 cord ; s., posterior sucker. 



