46 OLIGOCHAETA 



the finer anatomy of earthworms is better known than it is at present are in their 

 excretory system to some extent intermediate between the Megascolicidae that have 

 just been described and those in which the nephridia are paired ; there is a network 

 of fine tubes, but in addition to this a pair of larger nephridia which have a funnel 

 opening into the segment in front of that in which the tube lies ; a more remarkable 

 intermediate condition exists in those Cryptodrilidae which I place in a separate 

 genus Trinephrus, the name being suggested from the fact that they have three 

 pairs of nephridia in each segment of the body ; at present, however, the finer anatomy 

 of these worms is unknown, and we do not know the exact structure of these ne- 

 phridia ; a second intermediate condition is offered by the Geoscolecid genus Brachy- 

 drilus. In this worm there are two distinct pairs of nephridia in each segment of 

 the body. 



Finally, we have those forms in which there are only a single pair of these tubes 

 and they form the majority ; they include all the aquatic families, the Lumbricidae, 

 the Geoscolicidae (except Brachydrilus already referred to), all the Eudrilidae (where, 

 however, there is an integumental plexus to be referred to), and many of the 

 Megasoolicidae, the following genera (those genera in which all the species have 

 paired nephridia are marked with an asterisk) : Diporochaeta*, Perionyx*, Acantho- 

 driius*, Cryptodrilus, Megascolides, Ocnerodrilus*, Gordiodrilus*, Pygmaeodrilus*, 

 Pontodrilus* , Microscolex *. 



Connexion of nephridia with the alimentary canal. There are among the 

 Oligochaeta various organs of a glandular nature, opening into the alimentary canal, 

 which in some cases are certainty, in others probably, more or less modified nephridia. 

 These organs are invariably connected with either the front or the hind end of the 

 canal ; that is to say, they never communicate with that section which is undoubtedly 

 of hypoblastic origin. At the same time it cannot be said with absolute certainty 

 that those sections of the gut into which they do open are either stomodaeum or 

 proctodacum ; unfortunately embryological data are at present too scanty to permit 

 of a definite statement upon the point. In the present section I shall only deal 

 with those glandular appendices of the alimentary tract which are certainly, or 

 very probably, of nephridial nature ; I deal later with such organs as the calci- 

 ferous glands which cannot, with either probability or certainty, be referred to that 

 category. 



i. Peptoncphridia. I accept BENHAM'S term for nephridia opening into the 

 anterior section of the alimentary canal ; it seems probable that their function 

 is in relation to that of digestion. Such organs occur in more than one family 

 of the Oligochaeta. They were first made known in the Enchytraciclae, and 



