STAUROMEDUSAE. 



163 



cavity (Fig. 98). The ovum, according to Fol, undergoes a complete 

 segmentation, which results in a single-layered blastosphere. This 

 becomes an oval, two-layered larva, which becomes ciliated, swims 

 freely about, and finally attaches itself. The further development 

 probably takes place directly without alternation of generations. 



The Scyphomedusae are without exception marine animals, and are remarkable 

 for their great reproductive power. According to A. Meyer, if the stalk of 

 Lucertiaria be cut off, the cup reproduces a new one, and injured individuals, 

 and even excised pieces, can become perfect animals. 



Fio. 133. Tessera princeps (after Haeckel). o, external view magnified about 20 times; 

 6, longitudinal section through two perradii ; c, view of sub-umbrella. Gf gastral filaments ; 

 G gonads ; Rm circular muscle ; Sk septal unions. 



Sub-order 1. STAUROMEDUSAE. 



Without rhopalia, but in their place 8 simple principal tentacles (Fig. 133) 

 or marginal anchors (Fig. 134). Stomach with 4 wide perradial pouches con- 

 nected peripherally by a ring-canal. Gonads as 4 interradial horse-shoe shaped 

 thickenings (Fig. 133), or 4 pairs of adradial ridges in the ventral walls of the 

 gastric pouches (Fig. 134). 



