A Dr. A. Krohn on the Structure and 
tro-vascular system, which, according to my investigations, is no 
more wanting in it than in the umbrella-bearing Meduse, would 
of itself suffice to remove every doubt as to its true nature and 
position. This system is indeed much less developed than in 
the Medusz which lead a pelagic existence, but it neverthe- 
less consists, in accordance with the type, of radiating canals, 
six in number, corresponding with the arms, and of an annular 
vessel placed in the periphery of the body. The entire system 
is to be regarded as a lacunar excavation of the inner body-stra- 
tum (endoderm), which appears yellowish white by direct light, 
and brownish yellow under the microscope*. The best mode of 
obtaining a general view of this system is to bring the focus 
first of all upon the dorsal surface of the body, and then gradu- 
ally carry it deeper. It is then seen clearly that the six pro- 
portionally very wide but extremely short radiating canals spring 
from a sharply circumscribed discoid space occupying the bottom 
of the cavity of the body or stomach, from which they curve 
down along the radii corresponding with the arms, to open at 
last at the periphery of the body, into the perceptibly narrower 
annular vessel}. From the annular vessel a very nayrow and 
therefore very difficultly detectible canal is given off for each of 
the arms; this, running down in the axis of the arm, divides 
at the point of bifurcation into two branches, one of which pe- 
netrates each branch of the arm and reaches to its extremity {. 
In the axial canals of the arms, currents of a fluid filled with 
granules (chyle) may frequently be detected. They are un- 
doubtedly produced by the play of vibratile cilia, the effects of. 
which may readily be recognized from the granules seen here 
and there in rotatory or oscillatory movement. But they are 
* The Eleutheria is indebted for its yellowish-white colour to the endo- 
derm shining through the outer transparent layer (ectoderm). This colour 
has its seat in numerous roundish corpuscles imbedded in the endoderm, 
consisting, as already mentioned by Quatrefages, of an accumulation of 
very small granules. 
_ + The above-mentioned discoid space is in all probability a shallow ex- 
cavation of the bottom of the stomach, and may correspond to the chyle- 
receptacle detected by Gegenbaur (Grundziige d. vergl. Anat. pp. 82, 84, 
& 85) in several of the lower Medusz (Craspedota). 
{ Thearms of Eleutheria agree in structure with those of most Hydrozoa 
in their areolar or cellular tissue, the histological nature and physiolo- 
gical signification of which do not appear to have been yet satisfactorily 
ascertained. In Eleutheria, in which the axial canal extends through the 
midst of this tissue, the brown corpuscles already mentioned are seated on 
the compartments or cells immediately around the canal, although in very 
small quantity, from which we might be justified in regarding the entire 
tissue as a peculiar modification of the endoderm. I found it necessary 
to insert this remark here, because the views of M. Quatrefages as to the 
structure of the arms, which are also followed by Hincks, differ from mine 
in many particulars. 
