STRUCTURE OF THE LEECH. 195 



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 sperms pass outwards from 

 each testis by a short canal leading into a wavy longitudinal 

 male duct or vas deferens which gathers male elements from 

 each side. 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 the 

 narrow canal of the muscular penis, pass out on the middle 

 ventral line between rings thirty and thirty-one, and are trans- 

 ferred in copulation to the female duct of another leech. 



The female organs are more compact. The two small 

 tubular and coiled ovaries are enclosed in a spherical bladder, 

 the walls of which are continued as two oviducts which unite 

 together in a convoluted common duct. This is surrounded 

 by a mass of glandular cells, which exude a glairy fluid 

 into the duct. Finally, the duct opens into a relatively 

 large muscular sac — the " uterus," which opens through a 

 sphincter muscle on the middle ventral line between rings 

 thirty-five and thirty-six. 



The favourite breeding time is in spring. Two leeches 

 fertilise one another, uniting in reverse positions so that the 

 penis of each enters the uterus of the other. Spermatophores 

 are passed from one to the other, and the contained sperms 

 may remain for a long time within the uterus, or, liberated 

 from their packets, may work their way up the female duct, 

 meeting the eggs at some point, or reaching them even in 

 the ovaries. As considerable space has been given to a 

 description of the earthworm's development, I shall only say 

 that leeches present many similar embryonic features, con- 

 firming on embryological grounds what is otherwise probable, 

 that the Hirudinea are true Annelids. 



Classification — The Hirudinea include : — 



I. Rhychobdellidje, in which the fore-part of the pharynx can be pro- 

 truded as a proboscis. There are anterior as well as posterior 



