118 



EMnRTOLOGT 



observed that the scjphopolyps of Aurelia aurita, when 

 they are placed in unfavoui-able conditions (for example, in 

 aquaria), show little inclination to form poljdiscous strobila^, 

 but frequently develop only monodiscous strobilae (Fig. 59 

 A). In fact, Haeckel observed in certain cases that the 

 transverse division of the scyphopolyp metamorphosing 



into an Ephyra is altogether sup- 

 pressed, so that the entire body of 

 the larva is converted into the adult 

 animal. This is Haeckel's so-called 

 Ephyra pednncnlata (Fig. 59 B), which 

 was observed in the attached as well 

 as in the free-swimming condition. 

 Here therefore the alternation of 

 generations is omitted, and a simple 

 metamorphosis (hypogenesis) has 

 taken its place. 



The latter condition is the normal 

 and only one in Pelagia noctilnca, the 

 development of which has been made 

 known through Kkohx (No. 109), 

 KowALEVSKY, and Metschnikoff (No. 

 12). In this case there is first formed 

 a blastula which has a large cleavage 

 cavity, and soon becomes covered on 

 the sui'face Avith Uagella. At the 

 same time an invagination from the 

 posterior pole is formed, which leads 

 to the development of a gastral cavity 

 which does not by any means completely fill the space of the 

 primitive cleavage cavity (Fig. 60 A). The blastopore does 

 not close, but becomes the mouth of the larva. A shallow 

 depression is very soon noticeable at the posterior end of the 

 free-swimming larva, in the middle of which the part sur- 

 rounding the mouth projects in the form of a cone (Fig. 

 60 B). This projection becomes the oral cone of the Ephyra 

 (Fig. 60 C, m), and the circular depression surrounding it 

 the umbrellar cavity, while on the peripheral margin a divi- 

 sion into eight marginal lobes is soon noticeable, into which 



Fig. 59. — A, Strobila mo- 

 noilisca of Cyamea capillata 

 (after P. J. van Bknbdbn) ; 

 f, lobes of the Ephyra; t, 

 newly formed circle of 

 Scypliistoma tentacles on 

 the basal portion. 



B, Ephyra pedunculata of 

 Aurelia aurita (after IIaec- 

 kkl). 



