CH. i] RANGE OF PERICHiETID,E. 61 



The family Perichaetidae shows some remarkable 

 distributional facts. It may be divided perhaps into 

 five genera all of which have the complete or nearly 

 complete circle of setae which characterise the family; 

 but they differ in other particulars. Megascolex and 

 Perichceta have the nephridial system arranged in what 

 I have termed the diffuse fashion; they are in Mr 

 Benham's terminology " plectonephric." In them there 

 is not a definite series of paired nephridia, but an 

 infinity of minute tubes which open on to the exterior by 

 innumerable pores in each segment. On the other hand 

 Diporochceta and Perionyx have the normal paired 

 nephridia The genus Perichceta is also to be dis- 

 tinguished by the fact that very nearly all the species of 

 the genus have a pair of caeca arising from the intestine 

 at about the twenty-fifth segment. Now in Australia the 

 prevailing forms are Megascolex and Diporochceta. Peri- 

 chceta does occur, but there are not more than two or 

 three species. Diporochceta just gets into New Zealand. 

 As we pass from Australia into the Oriental region the 

 genus Megascolex is replaced by Perichceta which is the 

 prevalent type not only of the family but of earthworms 

 in general in the islands of the Malay Archipelago and 

 the continent of India. Megascolex however lingers on, 

 just fading away in Madagascar. The Oriental region is 

 further characterised by another genus Perionyx which 

 agrees with Diporochceta in the regularly paired nephridia 

 but differs in the fact that the glands into which the 

 sperm ducts open before reaching the exterior have a 

 coarsely lobate arrangement instead of being coiled tubes 



