Somo Plienomona of Regeneration in Liinnodrilus and related Forms. 425 



body wall. In the species being considered here and especially in 

 Tuhifex it appears first as two rather narrow parallel bands, one on 

 eacli sitlo of tlie ventral nerve cord or more accurately on each side 

 of the primordia of the ventral nerve cord. These are the ventro- 

 latcral bands (Fig. 15). Somewhat later the dorso-lateral bands appear 

 along the body wall, one each side of the coelom about on a level 

 with the Upper surface of the intestine. There appears to be some 

 doubt and divergence of opinion among investigators regarding the 

 origin of these bands. 



Abel (02), who also worked on Tuhifex, says that »die dorsal 

 gelegenen Teile der longitudinal musculature aus Zellen gebildet zu 

 werden schienen, welche sich hier vom Ectoderm loslösen und in 

 die Leibeshöhle einwandern«, v. Wagner also holds to this view. 

 Both of these authors as well as Hepke are of the opinion that the 

 nmsculature both dorsal and ventral is of ectodermal origin. 



AVhat has already been said on a previous page regarding the 

 supposed migration of ectoderm on the ventral side of the coelom 

 indicates that the results here obtained do not agree with this and 

 as for a migration of ectoderm into the coelom on the dorsal side 

 there seems to be still less evidence. The basement membrane of 

 the dorsal ectoderm always remains unbroken, unless injured by 

 accident, and indeed the cell proliferation and enlargement is but 

 shght in this region compared with that on the ventral side so that 

 the basement membrane is only slightly, if at all, disturbed. Cer- 

 tainly no ectoderm enters the coelom and Iwanow (03) seems to be 

 quite right in maintaining that »Aus den Elementen der Wandungen 

 der Cölomsäcke .... entstehen verschiedenartig gestaltete Mesoderm- 



gebilde, unter denen die Längsmuskulatur der Leibes wand «. 



The »Cölomsäcke« he derives from the neoblasts. An examination 

 of a cross section shows that by the division of the neoblasts smaller 

 cells are formed which move towards the dorsal side (Fig. 15 and 16). 

 They collect at the points where the dorso-lateral bands of longitudinal 

 muscles arise and undoubtedly give rise to these bands. Later others 

 go as far as the mid-dorsal line and there form the longitudinal muscles 

 of this region. There are also certain cells present in the dorsal portion 

 of the coelom which probably do not come from the neoblasts. Ran- 

 DOLPH was rather uncertain as to the origin of this "dorsal mesoblast". 

 Some divisions which she noticed in the dorsal peritoneum led her to 

 think they might have come from this source. Although such divisions 

 have not been noticed during the course of this work the character of 



