OF THE GENERATIVE ORGANS. 
423 
the centre of the disc ; the lateral crura are continuous with the substance of the disc 
above, and each meets with its fellow external to the centre of the disc, fig. 26. The 
central crura are united with these and thence with the disc by the thin membrane 
only. It thence follows that there exists above the central crura and the connecting 
membrane a wide crucial cavity ; into this the canals of the suspending pillars open, 
and from it radiate the canals which are given off to the circumference of the disc : 
the crucial cavity then is only a portion of the great system of canals. 
4/. The external surface of the outer half of the thin uniting membrane (which is 
composed solely of the two “foundation membranes”), is produced into a vast num- 
ber of transverse folds of a grayish -green colour in the male, but of a deep orange-red 
in the female, fig. 26. These give rise to the appearance of a coloured cross shining- 
through when the disc is viewed from above. The inner side of the folds is beset 
with a series of tentacles, the generative tentacles described above (31), fig. 30. In 
young specimens, not more than 3 inches in diameter, the generative organs were 
undeveloped ; the outer portion of the thin membrane being as smooth as the inner, 
but the series of tentacles already existed*. 
In adults the margins of the folds contain the spermatozoa in the male, the ova in 
the female. 
48. In the ovarium the ova lie between the inner and outer foundation mem- 
branes, which are both ciliated on their free surfaces. The ova are attached to the 
outer surface of the inner membrane by a kind of pedicle, which expands into the 
thick vitellary (?) membrane; this chorionic coat is distinctly cellular in middle-sized 
ova, in larger ones it is thicker and homogeneous. If the inner surface of the inner 
membrane be examined, a depression will be seen opposite each ovum : the yelk of 
the ova is granulous and of a bright orange colour. The germinal vesicle is clear 
and thin-walled, and is y^th of an inch in diameter ; the germinal spot is a thick- 
walled cell 3 - 3^0 q th of an inch in diameter, fig. 32. 
49. So far as the structure of the inner and outer membranes is concerned, the 
testis resembles the ovary. But the spermatozoa are contained in ovoid or pyriform, 
thick-walled sacs, about :^th of an inch in long diameter placed between the two,fig.31. 
In one individual the sperm-sacs were more ovoid in shape, and did not appear to have 
any particular attachment to either membrane, but in the rest they were all connected 
with the inner membrane, and when its inner surface was turned towards the eye, the 
* It appears to me that M. Milne-Edwards must have had a young individual of Rhizostoma before him, 
■when he says (Observations sur la Structure de la Meduse Marsupiale), “ Nor does the plaited membrane, which 
forms a sort of partition between the central and the four lateral cavities, appear to be an organ of reproduc- 
tion. If we examine one of these membranes superficially with the naked eye, we see towards its upper part a 
kind of woollen fringe, which at first sight might be taken for a series of glandular sacs, but by the aid of the 
microscope it is found that this appearance is due in fact to a multitude of suckers {su^oh's^, having the greatest 
similarity in form to those appendages which are observable in certain parts of the body of different Zoophytes, 
such as Vitella, Actinia, &c. From this it would appear that these membranes are much more fitted for 
absorption or respiration, as is the opinion of M. Eysenhardt, than for the formation of ova.” 
3 I 2 
