564 MONTGOMERY— MORPHOLOGY OF THE [April 34, 



(Graf, 1899), that develop from the splanchnic layer of the meso- 

 blast (Burger, 1902). 



Chloragogue (Botryo'idal Tissue). — Excretory cells placed upon 

 the blood vessels (Graf, 1893). 



18. Oligoch^ta. 



Adult Nephridia. — There are two main kinds of these which 

 it will be convenient to consider separately: meganepJiridia, larger 

 and in separated pairs ; and plectonephridia, networks of smaller 

 nephridia. 



MeganepJiridia. — Of these there is usually one pair to each trunk 

 segment, though exceptions are very numerous ; each has a preseptal 

 open funnel and a postseptal loop with intracellular cavity ; their 

 nephridiopores are usually separated and placed latero-ventral. The 

 smallest number known is two pairs (Bdellodrilus, Moore, 1897). 

 In Brachydrilus there are two pairs to each somite (Benham, 1888). 

 The anterior five pairs open into the pharynx in Dichogaster (Bed- 

 dard, 1888&), and probably also in Eniinca (according to Benham, 

 1890&, who terms this a " peptonephridium "). In Limnodrilus 

 the two anterior pairs perforate septa while the others do not 

 (Rybka, 1899). Libyodrilus is characterized by the nephridia 

 opening into a tubular system situated in the musculature, consisting 

 of four main longitudinal vessels extending from segment to seg- 

 ment and of segmental ring vessels, there being numerous excretory 

 ducts from the latter; this integumental network is secondary and 

 develops after hatching (Beddard, 1891). Numerous other devia- 

 tions from the general type are known that it is not necessary to 

 mention here, beyond the fact that nephrostomes are lacking in the 

 Chsetogastrids (Vejdovsky, 1885). 



Plectonephridia. — A plectonephridium is a complex that in each 

 segment is composed of numerous micronephridia, without nephro- 

 stomes, that are joined by a network of canals. In Acanthodrilus 

 there is one such micronephridium to each of the eight setae of each 

 posterior segment, and in each anterior segment there are about one 

 hunrlred nephridiopores; somewhat similar relations obtain in 

 Typhcciis (Beddard, i888n). In Megascolides there are a great 

 number of bundles of micronephridia which clothe the body wall 



