422 
MR. T. H. HUXLEY ON THE ANATOMY OF THE MEDUSA. 
a sort of eversion of the walls of the stomach, or more properly, of the central cavity. 
It consists in its upper or attached part of nothing more than the two “ foundation 
membranes,” and here they are smooth, but at their lower or free edge they become 
much plaited, acquire a deeper colour, and exhibit the characteristic generative ele- 
ments. Short tentacles, similar to those of Rhizostoma (31.), are scattered over the 
inner surface of each process, fig. 21 . 
43. In the ovarium, the two membranes develope between them immense multi- 
tudes of ova with a dark granulous yelk and clear germinal vesicle. The ova are 
attached to the outer surface of the inner membrane, the outer membrane passing 
quite freely over them, fig. 24. 
44. The testis is similarly composed of two membranes with an intervening space. 
The inner membrane is produced into a vast number of thick pyriform sacs, which 
lie between the two membranes, with their blind ends towards the inner surface of 
the outer membrane ; internally, they open each by a distinct aperture on the free 
surface of the inner membrane. 
45. The contents of the sacs are spermatozoa, and cells in every stage of deve- 
lopment towards spermatozoa. These stages are — 1 . Spherical cells, xFu^th of an 
inch in diameter, filled with smaller nucleated cells (fig. 23 d). 2 . Cells exactly 
resembling these included cells but free, and about 5 -^^th of an inch in diameter (&). 
3. Similar cells, occasionally united into masses with long filiform productions (c). 
4. Similar cells with a short process in the opposite direction also ; these swim about 
freely and sometimes move their tails {d). 5. Perfect spermatozoa with elongated 
heads (r^s-oth of an inch), rather larger below than above, where they are not more 
^han ^ 0 oop th of an inch in diameter, with very long tails of immeasurable fineness, 
extending from the larger extremity (e). From the existence of these different stages, 
I conclude that the spermatozoa are formed by the elongation of the secondary cells 
contained in the large cells first mentioned. 
46. I have not been fortunate enough to meet with any description of the gene- 
rative organs of the Rhizostomidse except that of these organs in Cephea by Will ; 
and as what I have observed differs somewhat from his statements, I will describe 
those of Rhizostoma mosaica somewhat fully. 
In this Acalephe, the eight arms which bear the stomachs are inserted into the 
lower angles of a thick square plate, which I have thence called the “ brachiferous 
plate,” fig. 27 . From the upper angles of this plate there arise four pillars, of the 
same structure as the peduncles of the arms, and are inserted into the under surface 
of the disc rather external to the middle point between its centre and margin. The 
‘‘brachiferous plate” has no other attachment to the disc, so that it forms the floor of 
an arched cavity, with four entrances between the suspending pillars of the plate. 
The suspending pillars expand at their attachment to the disc into three thickened 
ribs or crura, two of which are lateral and external, and one central and internal : 
these are united by a thin membrane. The central crura meet and form a cross under 
