278 PHYLUM ANNELIDA 



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 the narrow canal of 

 the muscular penis, and leave the body on the middle 

 ventral line between rings 30 and 31, when they are 

 transferred 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 spherical vesicles, 

 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 leads into a 

 relatively large muscular sac — the " uterus " — which opens 

 through a sphincter muscle on the middle ventral line 

 between rings 35 and 36. 



The favourite breeding-time is in spring. Two leeches 

 inseminate 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. The development is 

 direct. 



General Notes on Discophora 



The leeches constitute a relatively small class, whose structure has 

 been insufficiently worked out. The presence of suckers, the parasitic 

 habit, the reduction of the body cavity, have led many naturalists to 

 associate them with Flat-worms, but all recent work goes to emphasise 

 their affinity with Annelids, especially Oligochajtos. In leeches setae 



