— 196 — 
primitive tubes only. p,p Thickenings along the concret- 
ing edges of the sheaths of the small nerve-tubes. t Large 
nerve-tubes outside the scheath of which a neuroglia- 
nucleus is situated. 
Fig. 9. Nereis vir ens. (Magnified 950 diameters; Zeiss ViS' i-) 
Longitudinal section of a large nerve-tube (h) and some 
small nerve-tubes {nt) from the ventral nerve-cord. a Sheath 
of the large nerve-tube (b). The spongioplasmic walls 
of the primitive tubes of the nerve-tubes are distinctly 
seen longitudinal transsected. 
» 10. Nereis virens. (Magnified 950 diameters; Zeiss Vis» i-) 
Transverse sections of some large nerve-tubes running 
centrally along the ventral nerve-cord (compare fig. 14). 
a Central fibrous septum dividing the nerve-cord longi- 
tudinally into two lateral cords (cf. fig. 14). & & 6' Trans- 
verse bundles of neuroglia-fibres ; subdividing into branches 
{c, c). t, t Large central nerve-tubes. t^, ^2 h Somewhat 
smaller nerve-tubes, more ventrally situated. nt Small 
nerve-tubes. nt^ Small nerve-tubes situated between the 
large central nerve-tubes [t) and the central septum (and 
the transverse bundles of fibres \b]). h Neuroglia-nucleus 
situated in the ventral, reticular part (B) of the central 
septum [a). 
» II. Lumhricus agricoia. (Magnified 500 diameters; Seibert 
Vs, Zeiss 2.) Transverse section of the three colossal 
nerve-tubes (^i, t, t) and a part of the dotted sub- 
stance (c). a Connective-tissue outside the perineu- 
rium. h Perineurium (Vignals gaine troisiéme), outside 
which the layer of muscles (w, m) is situated. d Neu- 
roglia extending inside the perineurium, between the three 
colossal nerve-tubes. s, s, s Septa or very thick fibres 
occurring in this neuroglia and connected with the peri- 
neurium. c Dotted substance, exhibiting a reticulation 
produced by a transsection of tubes, nt Transsected 
nerve-tubes. k Neuroglia-nuclei. 
Plate IL 
Fig. 12. Ilomarus valgavis. (Magnified 330 diameters ; Zeiss. Apochr. 
4,0, — 0,45, I. Cam. lue.) Large nerve-tubes from an oeso- 
phageal commissure, seen in the live state in the commissure. 
