112 



EMBRYOLOGY 



The farther metamorphosis of the developing^ Scyphistoma 

 consists in a widening of the central stomach, whereby the 

 oesophagus gradually moves into the proboscis (Fig. 54 A), 

 and the gastral pouches tend to become obliterated. At the 

 same time the entrances to the four funnels, which are widely 

 open toward the peristome, produce a circular, groove-like 

 depression, involving the entire circumference of the origin- 

 ally flat peristome, which thereby approaches the bell shape 

 of the sub-umbrella of the medusa ; the proboscis, which has 

 become more elevated, corresponds to the oral tube [manu- 

 brium], while the gastral pouches, separated by the septa, 



represent the peripheral in- 

 testine {Kranzdarm) of the 

 medusa. The Scyphistoma, 

 by gradual metaviorphoses, has 

 approached in the most essential 

 featicres the structure of the 

 medusa (comp. Figs. 54 A and 

 57). 



Ill most of the other Discophora, 

 the development of the Scyphistoma 

 seems to take place in quite the 

 same way, especially in Cotiilnrldza 

 borbonira (Kowalevsky, Goette) 

 and Cyanea cajMata (Sars, Van 

 Beneden, Agassiz), where the eggs 

 likewise undergo the first stages of 

 development attached to the oral arms, and enveloped in a slimy jelly. 

 On the other hand, the early develoimient in Chryxaora, a form which 

 is also striking on account of its hermaphroditism, presents notable de- 

 viations (Glaus, No. 102 and No. 3). Here fertilization and the entire 

 embryonic development take place within the ovary, so that the larvaj 

 are not born until they reach the planula stage. The very small mem- 

 braneless eggs are surrounded in the ovary by a pedunculated follicle, 

 which owes its origin to the cells of the germinal epithelium. Fer- 

 tilization and cleavage are transferred to an early stage in the de- 

 velopment, so that at the same time with the embryonic development 

 there is a considerable growtli of the embryo as the result of a con- 

 tinual supply of food material on the part of the parent. This food 

 supply is provided by the follicular cells. In these particulars the de- 

 velopment of the egg and embryo of Chrysaora recalls that of the vivi- 

 parous Aphidic and the I'olyphemidffi among the Cladocera. In other 



Fig. 55. — Scyphistoma of Aurelia 

 aurlta. ph, proboscis ; tv, entrance into 

 the septal infumlibuliim ; t, tseniola;; 

 st, stalk; k, adhesive mass. 



