4OO 



HIRUDINEA 



their simplest form in such a type as Glossiphonia the lihyii- 

 chobdellae, to which this genus belongs, being indeed in most 

 particulars less specialised than the Gnathobdellae. Here 

 we have a distinct funnel opening freely into the median or 

 ventral coelomic space, which is immediately followed by a 

 rounded swelling termed by Oka l the capsule ; this is filled 

 with cells, in the interstices of which the ductules are situated 

 and meander. There is in this capsule a very strong likeness to 

 the glandular brownish swelling which immediately follows the 

 funnel in the nephridia of certain of the aquatic Oligochaeta, for 

 example the Naids, where, as Vejdovsky has shown, there is a 

 similar " rete mirabile " of the nephridial duct. After the capsule 

 is a single row of cells which are disposed in a complicated coil. 

 These cells are perforated by the duct, which is thus, as in the 

 Oligochaeta, intracellular. In the first set of cells the duct is 

 single, and gives off numerous branchlets into the interior of each 

 cell, a condition which has also been observed in many Oligo- 

 chaeta. Afterwards the cells are perforated by two, or even three, 

 main ducts, for the duct returns upon itself and traverses the row 



of cells more than once ; 

 there are also branchlets 

 developed from one or 

 other of the main ducts. 

 The terminal part of the 

 nephridiurn is a short 

 invagination from the 

 exterior, which is lined 

 by cells. There is 

 clearly a close resem- 

 blance here with the 

 nephridium of an Oligo- 

 chaete. The nephridium, 

 however, except for the funnel and the narrow tube immediately 

 following it, does not appear to be ciliated. 



There is, however, some difference of opinion as to the portions 

 of the nephridium where there are two ducts in a single cell. 

 Bourne 2 thinks that where there are two ducts there are two 



1 Loc. dt. 



2 Quart. J. Micr. Sci. xxiv. 1884, p. 419 ; see also ibid, xxxiv. 1893, p. 545, 

 which is mainly a criticism of Bolsius* additions to the very considerable litera- 

 ture upon the Leech nephridium. 



FIG. 207. Nephridium of Hirudo medicinalis. x 

 (After Bourne.) /, Funnel ; v, distal vesicle. 



