THE ANATOMY. SETAE 



' hastate.' The Enchytraeidae show another form of sigmoid seta which is nearly 

 perfectly straight but has not a cleft extremity. 



Another modification of the sigmoid seta is especially characteristic of the family 

 Geoscolicidae among earthworms, though not unknown elsewhere. The end of the 

 seta, which protrudes from the body, is ornamented (woodcut, fig. a a. 2, 3) with 

 transverse ridges [Pontoscolex) or with minute spinelets (Trichockaeta). 



The capilliform setae, (fig. 2, h. 2) which are exceptionally {Lophochaeta) covered with 

 fine processes (woodcut, fig. 3 &. 5), compar- 

 able perhaps to the ornamentation of the 

 sigmoid setae in Trichockaeta, to some 

 extent graduate into the sigmoid setae. 

 The intermediate condition is seen in 

 Phreodrilus, where the capilliform setae 

 are shorter, stouter, and more curved than 

 in other Tubificids. As Phreodrilus is in 

 other respects a link between the Tubifi- 

 cidae and Lumbriculidae, the fact gets 

 an additional intei'est. 



It sometimes happens that a worm has 

 setae of one kind only from head to tail. 

 This state of afiairs however is the less 

 usual. Among the aquatic forms certain 

 species of Aeolosoma, and of the Tubifi- 

 cidae (Limnodrilus), Enchytraeidae, and 

 Lumbriculidae, are the only instances. 

 Among earthworms the Moniligastridae, 

 many Megascolicidae, and some Lumbri- 

 cidae and Eudrilidae are examples. 



The commencement of a diversity 

 in the form of the setae is seen in 

 Phreoryctes, where some of the setae are 



^g. 2 a. I. OnycTiochaetavnndlei: -posterior seta. z. Ornamented 

 longer than the others — the dorsal longer seta of Geosooleoid. 3. IVichochaeta he^eridum. 3 b. End of 

 _ , 11' J.T. same more highly magnified. 



than the ventral, or mce versa, or the pos- ^.^ ^ ^ ^ ^^^^^ ^^^^ „f AmnmodHius georgianus. =. Spiw- 

 terior longer than the anterior: in many «'«''™»-''«''<'^- i. spiromrma fenx. 4. iiyodHiuscoccmeus. 5. 



® Lophochaeta ignota. 6. Tuoifex rivulorum. 7. Nazs ehnguis. 



Perichaetidae the ventraJmost setae are s. Nais eUnguU. 9. BohemUia comata. 



longer than the others ; in some those upon a few of the anterior segments are longer 



than the rest. 



Fig. 2, h. 



SETAE OP OLIGOCHAETA. 

 (After Vejdovsky, Stole, Miohaelsen.) 



