6 DESCRIPTIVE CATALOGUE OF THE 



3. THE LIFE-HISTORY OF THE SCYPHOMEDUS^E. 



The Jelly-fish are sexually differentiated, there are males and females. 

 Hermaphrodites have hardly ever been observed. The sexual products are 

 produced on the lower side of the umbrella, mostly in hernia-shaped exten- 

 sions of the gastral wall. Here we find certain zones where either spherical 

 ova in the female, or oval Spermasacs in the male, are found. In Chrysaora 

 females small sack-shaped serata are met with in the sub-umbrella wall. In 

 the female Pseudorhiza there are entodermal filaments, similar to the ordinary 

 gastral filaments scattered all over the entodermal surface in the canals of the 

 umbrella and arms, which appear filled with Spermasacs. Chrysaora females 

 sometimes do not produce any male products. Pseudorhiza seems to be a true 

 Hermaphrodite, no purely female specimens have been observed, nor do there 

 seem to be any males. It appears that also the Linergedre are Hermaphroditic 

 in a similar manner as Chrysaora. 



By the detachment of the ova they become free, and float about in the 

 gastral cavity. Here they are fructified. 



The ova may have a thick cell-wall with radial canals through it, a regular 

 zona pellucida or their cell-wall is thin. When free they are not surrounded 

 by a follicle which in some species, however, is present before birth. 



The Spermatozoa are very slender, and have a sharp spearhead-shaped head 

 and long tail. They are produced in great numbers in the Spermasacs by the 

 bursting of which they become free. They then swim about in the gastral 

 cavity of the male, and leave it after a little while. 



Copulation, which might be supposed to occur lias not been observed, as 

 stated above, however, the fructification of the ova takes place in the gastral 

 cavity of the female. The youngest stages are often found attached to the 

 moutharms or in portions of the gastral cavity. 



The gastrala is formed by invagination (Aairelia Chrysaora, etc.). Finally 

 a ciliated larva is formed, which has an oval shape and consist of high cylindri- 

 cal ectoderm cells and smaller cylinder cells in the interior. The one end, 

 which, as the larva swims about, is anterior, is devoid of cuidablasts. There 

 the ectoderm consists of high cylindrical gland-cells. These produce an adhe- 

 sive slime by means of which the larva attaches itself to a suitable surface. 

 In the ectoderm of the posterior end an abundance of cuidoblasts is met with. 



The larvre up to this stage are, in many species, carried about by the mother, 

 and there are often peculiar arrangements found for their protection. 

 In Cyanea annaskala the larvre arc attached to the entodermal side of the 

 moutharms in such numbers that this side may attain a white colour. In 

 Pseudorhiza aurosa peculiar sack-shaped appendages are found on the surface 



