210 
BOBEET SCHABEF. 
observed in Priapulus bicaudatus and Hamingia, 1 also in 
Sternaspis, 2 which, however, has now been removed from the 
Gephvrea. In Echiurus the cellular part of the nervous 
system is also arranged in form of two peripheral rows of cells. 
Immediately above the two masses of nerve-cells on each 
side of the cord the space seems filled up with connective 
tissue (fig. 6, h. p.) which would correspond to the great deve- 
lopment of the same in Priapulus bicaudatus (see Horst, 
fig. 15). Whether this is really connective tissue or whether 
the branches of the hypodermic cells assume a structure 
simulating connective tissue, I have not been able to settle. 
In the peripheral part of the central mass of nerve-fibres a few 
cells may be seen scattered here and there (figs. 6, 7, n.c) In 
the proboscis two longitudinal muscles appear on each side of 
the cord externally to the annular muscles (fig. 7, m.). The 
result is that the cord becomes compressed laterally and the 
two clusters of cells become fused into one (fig. 7, g. c .) 
A section through the nerve riug is shown in fig. 8. The 
ring, as we have seen before, is situated at the base of a 
groove ( g ), surrounding the mouth. The retractor muscles of 
the proboscis are attached to the ring, while it is itself again 
closely united to the skin by muscular tissue. The greater 
part of the nerve ring is taken up by fibres (f.) and ordinary 
cells ( g . c.), and the latter send their processes into the fibrous 
portion. A few larger cells lie above the fibrous part inter- 
nally (fig. 8, g,g.) 
The considerable swelling at the posterior end of the ventral 
nerve-cord has been very ably described by Horst with regard to 
Priapulus bicaudatus. I can only confirm his statements 
in the most essential points. His figure 14 is a very good 
representation of a cross section. The hypodermic cells send 
their branches to the interior from the peripheral part, while 
the central portion is taken up by smaller ganglionic cells, 
which are surrounded by larger ones. Such is the arrange- 
1 Daniellsen and Koren, loc. cit., p. 30. 
2 Sluiter, “ Ueber eineu indischea Sternaspis,” ‘Naturkundig Tijdschrift 
vor Nederl. Indie,’ vol. xli, p. 274. 
