A NEW GENUS OF OLIGOCH^TA. 485 



of the intestine. Such a discovery strengthens the current 

 opinion that the respiratory trees of Bonellia are really of 

 nephridial nature. 



A remarkable fact about these nephridia in Acantho- 

 drilus is the swollen terminal portion, which is lined by cells, 

 and which has the characters (fig. 10) of a diverticulum of the 

 gut. I have distinguished between the terminal section, which 

 opens into the intestine and is lined with an epithelium, identical, 

 so far as I can see, with the epithelium of the intestine, and the 

 next section, the cells of which are rather different. If the 

 nephridial tubes connecting this with the general nephridial 

 system were to disappear, we should have the gut furnished 

 with a series of tubular outgrowths ending bluntly. This is 

 exactly what we meet with in the Tracheata, and even in some 

 Crustacea — the Malpighian tubes ; these structures have been 

 compared with nephridia, particularly with the anal nephridia 

 of the Gephyrea. It appears that the Malpighian tubes of 

 Arthropods are formed by outgrowths of the proctodseum,! 

 though in the Amphipods Spencer is inclined to regard them 

 as appendages of the mid-gut. It is at least possible that we 

 may trace the Malpighian tubes of Arthropods to these gut 

 diverticula. Seeing how widely spread the Malpighian tubes 

 are among Arthropods, it is not unreasonable to seek for their 

 homologues in lower groups ; and the Chsetopods are the 

 nearest group to which we can trace the Arthropods. It is 

 true that Peripatus, which appears to stand somewhere near 

 the base of the Tracheate series, has no Malpighian tubes ; 

 this seems to imply a great break between the anal nephridia 

 of worms and the Malpighian tubes. It must be remembered, 

 however, that Peripatus is furnished with paired nephridia, 

 which structures are wanting in the Tracheata. Hence, there 

 might possibly be no need for the extra nephridia opening into 

 the extremity of the gut ; the ordinary nephridia being absent 



1 Recently Mr. Wheeler (19) has shown that inDoryphoradecemliueata 

 the Malpighian tubes, when first formed, open on to the exterior; they are 

 subsequently drawn in along with the proctodseal invagination of the ecto- 

 derm. 



