HIEUDINEA. 



397 



This is also the case with the ganglia of the ventral cord, and 

 especially with the siib-cesophageal ganglia, on which there are often 

 four longitudinal series of such ganglionic swellings, two median 

 and ventral, and two lateral projecting dorsally. The two 

 longitudinal trunks of the ventral ganglionic chain are invariably 

 closely approached to one another in the middle line, and 

 their ganglia are connected together in pairs by transverse com- 

 missures. In the Gnathobdellidce two nerve trunks are given off to 

 the right and left from each pair of ganglia, while from the brain 

 and the last ganglion, which may be called the caudal ganglion and 

 is formed of several ganglia fused together, a much greater number 

 of nerves pass off. The nerves passing off from 

 the brain supply the sense organs and the mus- 

 cles and skin of the cephalic disc (ancerior 

 sucker) ; the nerves of the ventral chain are 

 distributed in their proper segments, (and those 

 of the terminal ganglion supply the ventral 

 sucker. An unpaired median longitudinal cord 

 (Faivre, Leydig), which passes from ganglion 

 to ganglion between the two halves of the ven. 

 tral cord, most probably corresponds to the 

 unpaired nerve which Newport discovered in 

 insects. A system of visceral nerves was dis- 

 covered by Brandt. It consists of an intestinal 

 nerve, which arises from the brain and runs 

 close to and above the ganglionic chain and 

 sends branches to supply the caeca of the in- 

 testine. Three ganglia, which in the common 

 leech lie in front of the brain and send their 

 nerve plexuses to the jaws and pharynx, are 

 considered by Leydig as enlargements of cere- 

 bral nerves and very likely control the move- 

 ments which occur in swallowing. 



Almost all leeches possess simple eyes on the 

 dorsal surface of the anterior ring. In addition there are cup-shaped 

 organs (in Hirudo medicinalis about sixty) on the cephalic rings. 

 These probably give rise to a sense perception comparable to the 

 sensation of taste. 



Generative organs. The Hirudinea, are hermaphrodite. As in 

 many marine Planaria, the openings of the male and female 

 generative organs are placed one behind the other in the middle 



FIG. 322. Generative 

 apparatus of the Med- 

 icinal Leech. T, Tes- 

 tis ; Vd , vas deferens ; 

 Nk, epididymisj Pr, 

 prostate ; C, cirrus ; 

 Ov, ovaries with vagina 

 and female genital 

 opening. 



