No. 2.] THE MORPHOLOGY OF DERKO VAGA. £7! 
of the body, and, furthermore, that there is a gradual shading 
off from the first ganglion to those in the middle region of the 
body. The sense organs I have been able to trace in lines 
extending the whole length of the worm. Posterior to the fifth 
segment the glandular bands and dotted grooves occur on every 
segment. I have not been able to trace them to the first seg- 
ment. The first five segments contain certain organs which 
are necessary for the proper maintenance of the life of the 
worm, and it is not improbable that this differentiation may 
account for a partial obliteration of the metameric features in 
this region. 
2. SEGMENTAL SENSE ORGANS IN ANNELIDS AND ORGANS OF 
SPECIAL SENSE IN HIGHER ANIMALS. 
’ 
From the discussion of the so-called ‘lateral line”’ in anne- 
lids it now appears that there can be no homology between 
annelids and vertebrates based on this structure. It will be 
well, however, to call to mind other lateral-line homologies 
which have been suggested by several writers who take the 
segmental sense organs as a basis for comparison. 
In 1879 Eisig threw doubt on the homology instituted by 
Semper, and considered that the segmentally arranged sense 
organs of the Capitellidae were homologous with the sense 
organs of the lateral-line system found in fishes and larval 
batrachians. 
In 1887 he affirmed his former view and cited in support 
of his homology the work of Meyer on Polyophthalmus and 
Beard+ on sense organs of the lateral line in vertebrates. 
Professor Whitman in 1884? and again in 1889? suggested 
that the segmental sense organs of the leech are identical with 
the lateral-line organs of the vertebrates. He further suggests 
“that the segmental sense organs of annelids have formed the 
1 J. Beard, On the Segmental Sense Organs of the Lateral Line, etc., Zool. 
Anz., Bd. VII, 1884, pp. 123-140. 
2C. O. Whitman, Segmental Sense Organs of the Leech, 4m. Wat., Vol. 
XVIII, 1884, pp. 1104-1109. 
3 Jézd., Some New Facts about the Hirudinea, Journ. of Morph., Vol. I, 1889, 
PP- 592-595: 
