354 
REVIEWS. 
Professor Agassiz lias here given might be obtained. All this we 
may admit, and still attach a high value to the copious record of 
independent investigations now before us. 
a.—Aurelia Jlavidula so nearly resembles its European congener, 
A. aurita , that the specific distinctness of the two appears to us by 
no means proven. This, the commonest of all “jelly-fishes,” though 
not a stinging species, is, at the same time, rather an aberrant than 
a typical member of its group. Its marginal tentacles, veil-like mem¬ 
brane, and circular canal, in possessing which it differs from the 
majority of Phanerocarpce, are so many points in which it agrees with 
the lower Medusae. On the other hand, according to Professor Agas¬ 
siz, very old specimens of Aurelia show some degree of approxima¬ 
tion, however remote, to the Rhizostomidce. The Hydra-tuba observed 
by Reid belongs to this genus, but Professor Agassiz asserts that the 
canal-system, described by that anatomist, does not really exist, its 
four radiating elements being solid longitudinal ridges (long before 
noticed as such by Siebold), while the circular vessel is wanting. 
The canal-system of the mature Aurelia Professor Agassiz describes 
with a view to his own theory of the homologies of its parts. It is 
usual to recognize sixteen canals, starting from the central cavity, of 
which eight run, without branching, to points on the circular vessel, 
midway between the marginal bodies, while each of the eight other 
canals supplying these last gives off, close to its origin, a pair of 
vessels which again and again sub-divide on their way to the margin, 
the branches thus formed becoming reconnected by anastomosis.* 
Professor Agassiz, however, regards the radiating canals as consisting 
of eight different systems ; namely, four simple, or “ ambulacra!,” and 
four more complex “ interambulacral ” systems. It must be re¬ 
membered that the four extensions of the central cavity which con¬ 
stitute the genital chambers alternate with the oral appendages and 
with four of the (eight) marginal bodies. Now, the four ambulacral 
systems are those which issue directly from the central cavity and 
correspond, therefore, with the four mouth corners; while the inter¬ 
ambulacral systems appear to arise from the outer edges of the genital 
pouches between them. 
“ From each corner of the month, and between two adjoining genital pouches, 
arises one main radiating tube, extending straight to one of the marginal indenta¬ 
tions, without lateral ramifications, except from near its base, on each side of which 
arises one branch which divides again and again, anastomosing among themselves. 
Of such systems there are, normally, only four.” 
“ The systems which correspond to the radial prolongations of the genital 
pouches are far more complicated: in the first place, the sexual pouch itself must be 
considered as a sack-like enlargement of this radiating system, and from the outer 
wall of this sack arise the peripheric radiating tubes belonging to it, three of which 
are simple, and extend directly to the margin without ramifications. The central 
one extends from the middle of each genital pouch to the corresponding marginal 
indentation; the outer ones, bordering each genital system, arise independently near 
* See the drawing by Milne Edwards, in his “Recherches anatomiques et 
zoologiques faites pendant un voyage sur les cotes de la Sicile.” 
