No. 2. ] THE MORPHOLOGY OF DEKO VAGA. E57 
segment, and, as development proceeds, it is pushed back to 
the third. From this we may infer that the former condition 
is more primitive than the latter. The shape of the dorsal 
ganglion differs in different species. In Dero vaga it is very 
simple, much more so than in other Naidomorpha and in 
Tubificidae, and resembles somewhat the dorsal ganglion in 
Lumbricidae. 
From descriptions of the nerves given off from the dorsal 
ganglion the number varies greatly. This may be due largely 
to insufficient investigation and difference in interpretation as 
to the origin of the nerves found. I think it highly probable 
that the number of nerves given off from the dorsal ganglion 
in any case will be found to correspond with the number given 
off from each ventral ganglion. This correspondence exists 
in Dero and Beddard ! states that a similar condition exists in 
Spirosperma. In most earthworms there appear to be three 
nerves from the dorsal ganglion and three from each ventral 
ganglion. The third nerve in each segment, however, sends 
off a branch which goes to the dissepiment. Further investi- 
gation is necessary before we can compare the nerves of the 
dorsal ganglion of the earthworm with the lateral nerves from 
the ventral cord. 
I believe that the arrangement of nerves which I have 
described for Dero vaga will be found to hold good for the 
majority of forms in the families Naidomorphaand Tubificidae. 
The observations of Vejdovsky? and Stolc3 on Tubificidae point 
in this direction. While Vejdovsky figures five nerves to a 
segment, it is not improbable that the two going to the dissepi- 
ment are really one. Stole describes one to the dissepiment 
and three others within the segment. 
1 Beddard, Z.c., p. 20. 
2 F. Vejdovsky, System und Morphologie der Oliogochaeten, Prag, 1884, p. 85. 
Pl. VIII, Fig. 2. 
3 A. Stole, Llyodrilus coccineus Vejd., Ein Beitrag zur Kenntnis der Tubificiden, 
Zool. Anz., Bd. VIII, 1885, p. 641. 
