654 OLIGOCHAETA 



This genus is one of the most widely distributed ; its wide distribution is all the 

 more remarkable from the fact that there are at most only three species known. 

 SCHMARDA found it upon the sea-shore of the island of Jamaica, in company with 

 Diackaeta littoralis and Pontodrilus. MULLER recorded it from Brazil. PERRIER'S 

 specimens came from Martinique, Gloria, Brazil, and, lastly, from Java. HORST and 

 ROSA received the genus from Sumatra and from Nias. I have had examples from 

 the following widely separated localities : British Guiana, Hawai, St. Vincent, 

 Singapore, Australia, Andaman Islands. It is, therefore, characteristic of the tropics 

 of both the Old and New Worlds, with the exception of Africa from which continent 

 it has not yet been obtained. 



The most salient external character of the genus Pontoscolex is the irregular 

 disposition of the setae upon the posterior segments of the body; upon the first few 

 segments the setae are regularly paired ; but by gradual degrees the setae get 

 further apart and do not correspond in successive segments ; finally, on the segments 

 at the hinder extreme of the body, the eight setae of each segment regularly 

 alternate in position from segment to segment, producing the impression that there 

 are more than eight setae per segment. These posterior setae are rather larger than 

 those upon the head segments, but the difference in size is by no means so pro- 

 nounced as it is in the genus Onychochaeta. The setae are, as is so frequently the 

 case with the earthworms of the family Geoscolicidae, ornamented at the free 

 extremity with transverse ribs ; the clitellar setae are rather longer and straighter 

 than the ordinary setae. Pontoscolex is unique among earthworms in having setae 

 which are bifid at the free extremity, as in the Tubificidae and many other families 

 of aquatic Oligochaeta. 



The clitellum is saddle-shaped ; it occupies segments xv-xxi (or thereabouts). 



The tiephridiopores are lateral in position ; they do not, owing to their shifting 

 in successive segments, always correspond to a seta. 



There seem to be no dorsal pores. 



The alimentary canal of Pontoscolex has a gizzard and three pairs of calciferous 

 glands ; the intestine has a typhlosole which occupies only the middle region ; there 

 are four specially thickened septa which separate segments vi/viii and x/xi, the 

 intermediate septum being entirely absent. 



A very distinctive feature of the genus Pontoscolex is the existence of peculiar 

 sense organs, or rather bodies of unknown function in the epidermis ; these were 

 first discovered by PERRIER, and are figured in his memoir upon ' Urochaeta ' already 

 referred to. They are round, highly refracting corpuscles, furnished with a nucleus ; 

 they stain deeply with borax carmine, and are thus always very conspicuous in 



