254 A, A. W. HUBRECHT. 
ence in the cephalic sacs (Keferstein’s side organs) probably 
goes alon® with this, as I wili further on endeavour to show. 
‘ton ly the ganglia are ofa red colour, paler in the Om- 
matopleans, much deeper and richer in the largeenoplan forms, 
suchas Meckeliasomatotomus, Meckelia Ehrenberg., &c. To the 
kindness of Mr. Ray Lankester, then also at the Zoological 
Station, I am indebted for the use of his excellent microspec- 
troscope, which, applied to the diffused colouring matter of 
these nerve-centres, left no doubts about its chemical con- 
stitution. It showed the two absorption-bands of oxyhemo- 
globin with great distinctness. Mr. Lankester had found a 
few years ago hemoglobin in the ventral nerve-chain of 
Aphrodita, and the curious fact of its occurrence in nerve 
tissue now stands isolated no longer. It must be observed 
that in the same species which showed this so strongly the 
blood was quite colourless and devoid of corpuscles, which 
are tinged by hemoglobin in some other Nemertean species, 
as mentioned above. 
Investigations into the minute histological structure of the 
four lobes of the ganglion, soldered together in front by the 
superior and inferior commissures, show that a_ thick 
bundle of exquisitely fine fibres occupies the middle of each 
lobe. A thick layer of nerve-cells surrounds this kind of 
axis on allsides. ‘These nerve-cells are imbedded in a neuri- 
lemma-sheath, as described by Leydig', and vary in size. The 
smaller ones are the more numerous, still the larger ones 
occur very regularly, often attaining a diameter of 66 mm. 
The central fibrous bundles of each of the four ganglionic 
lobes unite in the commissures, forming a closed ring. ‘Those 
of the inferior lobes continue their course backwards in the 
nerve-trunks, those of the superior lobes penetrate without 
interruption into the tissue of the cephalic sacs, which lie 
behind these lobes in immediate contact with them, ending 
there. 
The lateral nerve-trunks, whose different position in the 
Borlasians and in the Ommatopleans has been clearly pointed 
out by Mr. MacIntosh, show two different constituent ele- 
ments, viz., (1) the above-mentioned central bundle of fibres, 
and (2) a sheath of nerve-cells, thicker in the vicinity of the 
ganglia, thinner further backwards, but accompanying the 
trunk in its entire length. The size of the nerve-cells agrees 
with that of the smaller cells in the central ganglia. Mr. 
MacIntosh has not remarked this cellular coating. He 
speaks of a fibro-granular matrix of a reddish hue enclosing 
the nerve-trunks. ‘The red colour is caused by these nerve- 
1 ©Vom Bau des thierischen Korpers,’ p. 86. 
