ACALEPaa:. 181 



testis from a fresh male medusa, place it on a watch-glass with the 

 under surface, on which the sperm-sacs open, uppermost, when if 

 the Acalephe is in the rut, the escape or emission of the spermatozoa 

 may be seen. The development of the sperm-cells is not always 

 according to the size of the animal; they have been found, fully 

 formed^ in medusae one inch and three-quarters to three inches broad, 

 and even a specimen of one inch in diameter had active spermatozoa 

 in the testes. 



The coloured frill in the generative cavities forms in the female, as 

 in the male, the essential generative apparatus. The ovarium, like 

 the testis, consists of a band, with many folds, attached to the septum 

 dividing the generative from the digestive cavities ; it has a proper 

 peristaltic motion ; its concave border is beset with similar tentacles, 

 which are extensile and flexible in all directions, are armed with 

 many urticating cells and are beset with vibratile cilia. The thin 

 epithelium on the under surface of the ovarium is here and there 

 slightly ciliated, which has not been observed in the testis. The 

 tissue of the ovarium is looser than that of the testis, and the band 

 has more the appearance of a flattened tube ; but the ovarium is not 

 a simple folded sac, with an oviducal opening, as Ehrenberg supposed. 

 The minutest germs of the ova are nearest that surface of the 

 ovarium which is attached to the membranous septum : as the 

 germinal vesicles acquire their vitelline investment they approach the 

 opposite or free surface, from which the mature ova protrude, covered 

 only by a very thin membrane, and giving a coarse granular character 

 to that part of the ovarium. The germinal vesicle has its spot, or 

 nucleus ; the surrounding yolk, as it accumulates, becomes violet 

 coloured. It is covered by an extremely delicate membrane with 

 a smooth surface. In this state the ova are transferred from the 

 ovarium to the marsupial sacs ; but how they get there is not known ; 

 they are doubtless impregnated i/i transitu. In the marsupial ova 

 one can no longer discern the germinal vesicle ; it has combined 

 with the matter of the spermatozoa and become diffnsed through 

 the yolk. The primary germ-cell, developed most probably as in the 

 Ascaris, from the impregnated nucleus of the germinal vesicle, at- 

 tracts the whole germ-yolk about it, and divides it progressively 

 with its own divisions. The first division of the yolk resembles the 

 spontaneous fission of some infusorial monads, inasmuch as it begins, 

 not at every part of the circumference, but on one side (^g. 80.), and 

 proceeds across to complete the bipartition {Jig. 81.). Subsequent 

 subdivisions, corresponding with those of the ova of the Ascaris 

 (p. 113.) are described and figured by Siebold, from whose memoir* 



* LV. tab. i. 

 N 3 



