ON AMPHIPORUS SPECTABILIS. 287 
represented), I have only to state that in the adult they 
appear to have their proper investment all round, except 
where it is indented in the preparations by the prominent 
posterior fibrous cornu of the ganglion, from which (cornu) 
each probably receives supply. Further, instead of being in 
doubt on the subject, I am now inclined to consider these 
sacs as special sense-organs. It is indispensable in such 
researches to examine an extensive series of favourable 
living forms, some of which show these organs very 
distinctly. Again, it is also necessary to consult those 
in which they are wholly absent, e.g., Cephalothrix, as 
well as their appearance in such forms as develop new 
heads on fragments of their bodies, e.g., Lineus sanguineus. 
But the most crucial evidence in support of our view 
that, though closely connected with the ganglia in the 
adult, the cephalic sacs are structures sui generis in Lineus 
gesserensis, is that afforded by the young animal in the course 
of its development. The careful examination of Pl. X XIII, 
fig. 9. (op. cit., Ray Society) will show those organs (m) very 
considerably posterior to the ganglia, and it is observed that 
their gradual advance in position, and proportional diminu- 
tion in size as age increases, are interesting features. Dr. 
Hubrecht’s remark about abnormal tension as the cause of 
the separation in Lineus gesserensis will not, I fear, apply to 
the various sections, horizontal, vertical, and transverse. 
The finding of hemoglobin (which was formerly, and with 
propriety, called red colouring matter) is interesting ; but as 
the same red colouring matter accompanies the nerve-trunks 
in many forms without any access to the sea-water, and as 
Dr. Hubrecht will probably find it in abundance in the great 
red muscles of the body-wall, and in the fluids of Borlasia 
Elizabethe (op. cit., Ray Society, p. 97), some caution in 
predicating functionally of the cephalic sacs in this respect 
is necessary. 
The second point under this head is Dr. Hubrecht’s asser- 
tion that ‘‘a sheath of nerve-cells, thicker in the vicinity of 
the ganglia, thinner further backwards,” accompanies the 
lateral nerve-trunks, and that I had not remarked this cellular 
coating. If, however, for example, Pl. XXI, fig. 6 (op. cit., 
Ray Society), be examined, this coating is represented as 
sufficiently cellular (x'700 diam.). In transverse sections 
of large examples of the Linzipm, nothing can be more 
evident than this investment of the lateral nerve-trunk, 
which is deeply tinted by the reddish colouring matter 
—a feature very boldly seen in Borlasia Elizabethe, whose 
muscles are likewise reddish. As Dr. Hubrecht and my 
U 
