ON THE ANATOMY OF THE FAMILY OF THE MEDUSAE 21 



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. 



47. The external surface of the outer half of the thin uniting mem- 

 brane (which is composed solely of the two " foundation membranes "), 

 is 'produced into a vast number 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 founda- 

 tion membranes, 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 Tj^-o-th of an inch in 

 diameter ; the germinal spot is a thick-walled cell -j-jyoth 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 -g-Vth of an 

 inch in long diameter placed between the two, fig. 31. In one indi- 

 vidual 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 



1 It appears to me that M. Milne-Edwavds must have had a young individual of Rhizostoma 

 before him, vifhen 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 reproduction. If we examine one of these mem- 

 branes 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 [sufoirs), 

 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. Eys;nhardt, than for the formation of ova." 



