226 Froceedings of the Royal Society of Victoria. 



Connected with the alimentary canal is a paired structure 

 which, as far as I know, has not been found in any leech hitherto 

 described (Fig. 17, P.O.) This doable "posterior organ" lies on 

 the ventral sui-face just beneath the stomach in somite XIX. 

 The two halves can be distinguished as riglit and left posterior 

 organs. They lie very close together in the mid-ventral line 

 above the nerve cord, and extend from the tifteenth to the 

 sixteenth ganglia, measuring 2 '024 mm. in length. 



Their external appearance is that of elongated narrow bodies 

 with longitudinal markings of black pigment (Fig. 17, p.g.). 

 Examined microscopically they are found to be exceedingly 

 glandular organs. The internal surface is thrown into numerous 

 folds (Fig. 18, Fid.) by the growing in of the blood vessels, thus 

 greatly increasing the glandular surface and giving rise to the 

 external longitudinal markings. It is difficult to obtain sections 

 in which the histological structure of this organ can be well 

 determined. The folds are lined by a single layer of modihed 

 columnar cells which are vacuolated at the end facing into the 

 cavity of the organ, their outer ends staining deeply. Only very 

 rarely can nuclei be detected. 



The blood supply is very rich, vessels passing along the 

 longitudinal grooves and ramifying everywhere through the 

 structure. Slightly towards the inner side of the middle line at 

 the posterior end of each organ a duct opens (Fig. 17, D.P.O.), 

 and is continued back on each side of the stomach and intestine 

 to the eleventli diverticulum of its own side. 



Here it passes into the diverticulum (Fig. 19, D.P.O., Dvt. 11) 

 almost at the extreme posterior end and on the inner side. The 

 duct is formed of closely set columnar cells surrounded by 

 connective tissue. (Fig- 19, Col. epi.) With regard to the 

 function of these organs I am unable to offer any suggestion 

 except they are without doubt glandular. 



Vascular System (Figs. 20, 21 and 22). 



The blood is red and consists of plasma and corpuscles. 



In Phihemon as in Hirudo there are four main longitudinal 

 trunks, viz., the dorsal and ventral sinuses, and the two lateral 

 blood vessels. 



