204 
being situated outside the somatic layer of the mesoderm 
Surrounding the coelom. The latter mesoderm might be 
compared then to the lateral plate of Chordates. All thís 
is shown by fig. 4, reproduced from HATSCHEK (1878, 
fig. 89). Also in Scoloplos 1 (1916, fig. 69, 70) found similar 
figures in transverse sections and was struck by the 
resemblance in their situation to that of the myotomes. 
The rudiment of the dorsal longitudinal musculature 
is much less. conspicuous. 1 feel inclined to see in the 
rudiment of the ventral longitudinal musculature, being by 
far the most important component of the musculature of an 
Annelid, the beginning of the voluntary longitudinal mus- 
culature of the trunk of Vertebrates, as suggested equally 
by HATSCHEK (1878, p. 117). We can only suggest that the 
dorsal longitudinal musculature of Annelids, already less 
developed here than the ventral, has been lost in Vertebrates. 
To the circular muscles of Annelids the musculus transversus 
of Amphioxus shows a certain resemblance, consisting also 
of circular muscle fibres while it is innervated by the 
dorsal spinal nerves. The position, it is true, cannot be 
directly compared to that of Annelids. 
Double innervation. — As to the innervation of the longitu- 
dinal musculature of Annelids FRAIPONT (1884, p. 280—281, 
1887, p. 36), studying Polygordius, Protodrilus and Saccocirrus, 
observed in all these forms in the longitudinal muscles a 
diffuse nervous plexus which is not only connected with 
the ventral ganglion chain but also directly with cells of 
the epidermis, as could be shown in sections and by 
dilaceration. As a consequence of this double innervation 
“les impressions regues de l'extérieur peuvent être trans- 
mises directement aux cellules ganglionnaires du plexus 
intermusculaire, sans avoir besoin de passer par les éléments 
centraux de la moelle.” In the posterior region of the body, 
where the ventral medulla is no longer found, the second 
mode of innervation is even the only one that is present. 
It would be extremely interesting to know if also the 
ectoderm of the stomodaeum possibly stands in a similar 
relation to the intermuscular plexus. For after the stomodaeum 
ad grown out to the medullary tube of Vertebrates and 
had extended along the neural surface of the body, similar 
relations may easily have been established between it and 
the contiguous lateral musculature. I feel inclined to suppose 
that in this way the ventral spinal roots, at first in a more 
