PHYLUM ANNULATA 



511 



goes an immediate change, its 

 colour turning from red to 

 green. The digestion of a 

 whole cropful of blood takes 

 many months. The stomach 

 is continued into a narrow in- 

 /tsfi/ie (int.) : this passes into a 

 somewhat dilated rectum (ret.) 

 which turns slightly upwards 

 and opens by the anus (an.) 

 in the last annulus. 



The excretory system 

 consists of seventeen pairs of 

 nephridia (nph. 1-17), situated 

 in segments 7-23. A typical 

 nephridium (Fig. 409) has the 

 general form of a loop passing 

 upwards from the ventral body- 

 wall, produced into an off- 

 shoot which extends inwards 

 (mesially) to the correspond- 

 ing testis, and connected pos- 

 teriorly with a small bladder 

 or vesicle (vs.). The principal 

 loop is divisible into two chief 

 parts, the main lobe (m. I.) and 

 the apical lobe (a. I.), connected 

 with one another by a short 

 recurrent lobe (r. I.): the off- 

 shoot to the testis is known as 

 the tcstis-lobc (t. I.) ; it is absent 

 in H. australis. 



All these parts are formed 

 of a close-set mass of gland- 

 cells, traversed by a complex 

 system of minute intra-cellular 

 passages or ductules, which 

 finally unite into a compar- 

 atively wide inter-cellular tube 

 or duct : this winds through 

 the main and apical lobes, 

 and finally enters the vesicle, 

 which opens posteriorly in the 

 last annulus of the segment. 

 The free end of the testis-lobe 

 is swollen into a lobed mass 

 which lies in a sinus (Fig. 

 405 nst) in comiection with 



