DISCOPHORA ; DEVELOPMENT. 



537 



become deeper, their edges display eight notched processes (/), 

 and as the separation grows more and more distinct, the seg- 

 ments at last resemble a pile of jagged saucers placed one upon 

 another. Finally these segments separate from each other and 



FIG. 725. DEVELOPMENT or MFDUSA. 



swim away freely, when they present a conformation somewhat 

 resembling that of a Medusa, although the notched processes 

 give it the appearance of an eight-rayed star. By degrees 

 these shorten until the disk becomes nearly circular, when the 

 mouth and other organs belonging to the stomachal peduncle 

 make their appearance in the centre (#) ; the buccal tentacula 

 are afterwards developed, a^nd the animal soon acquires its ma- 

 ture form. In the naked-eyed Medusae, as far as our present 

 knowledge extends, the Polype produced from the ciliated embryo 

 is of the Tubularian type, and the Medusae are produced by true 

 gemmation from the neighbourhood of the tentacula. They 

 first appear in the form of small rounded knobs, which in- 

 crease in size, and acquire more and more of the form of 

 the Medusa; the pedicle by which they are attached to the 

 parent Polype at the same time grows thinner by degrees, until, 

 when the Medusa has attained its perfect form, it drops away 

 from its point of attachment, and swims freely through the 

 water. In some cases, however, there is a direct production of 

 Medusae from Medusae, either by gemmation or by ova. Thus 



