172 PRACTICAL PARASITOLOGY 



epididymis ; they then form the muscular ductus ejaculatorius, which 

 is continued on to form the penis. The base of the penis is swollen 

 into a kind of bulb which contains numerous prostate glands. 



With regard to the nervous system, it will be sufficient for the 

 student to make himself acquainted with its anterior portion, that 

 is to say, with the circumcesophageal ring. The pharynx should be 

 carefully loosened without damaging the nerve-cord lying beneath it. 

 The longitudinal section of the body- wall should be continued forwards 

 until the pharynx is quite freed from the dorsal wall. If the pharynx 

 is now pulled sharply backwards the two upper pharyngeal ganglia 

 will be seen lying upon it. They will appear as two rounded blackish 

 bodies of about the size of a grain of linseed. If the pharynx is now 

 cut through above the two ganglia and pulled forwards, the entire 

 oesophageal ring will be seen. The central nervous system is remark- 

 able for the fact that the ladder-like arrangement is modified by the 

 position of the ganglia. The two ganglia of each segment are so 

 close together that they appear to be one. Owing to the reduction 

 in length of the segments to which they belong (seen externally by 



the smaller number of annulations), the 

 ^uiu. anterior and posterior ganglia are also 



very close together, while those in the 

 fully developed five-ringed segments 

 are considerably farther apart. 



The three jaws should be removed 

 from the oral cavity and examined 

 under the microscope upon a glass slide. 

 They are plane objects, nearly semi- 

 circular in shape, the curved edge being 

 FIG. 87. a, Anterior end of furnished with minute teeth, which may 



Eirudo. The oral cavity is open and b e seen w ith a low-DOWer lens. The 

 shows the three jaws, b, A jaw with , ., , ,1 .!_ 



muscular attachment very strongly number ot these teeth varies within 

 magnified. (After Glaus.) certain limits. Between them are the 



orifices of the salivary glands, the 

 secretion from which prevents the coagulation of blood. 



Sections should be prepared from leeches which have been well 

 stretched and thoroughly hardened. The animals should be killed in 

 acetic acid solution of chromium, stretched, cut into several pieces, 

 which are returned to the fixing fluid and allowed to remain in it for 

 several hours ; these are then rinsed, dehydrated, hardened in alcohol 

 by graduated stages, and cut, either by hand or with the microtome. 

 A transverse section taken from the middle of the body will show the 

 following conditions : externally is a thin cuticle, beneath it a single 

 layer of epithelium, between the cells of which pigmented connective 

 tissue and blood-vessels are sometimes seen ; within this is a thinner 



