HYDROZOA. 



57 



larger and commoner kinds of Jelly-Fish or Sea-Xettles. A brief Case 3, 

 accoimt is given below of AureUa aurita* (Model and specimens ^P"^^* P^""*' 

 in Case 3), whose phantom disks are so often seen in summer 

 time slowly swimming below the surface. In the centre of the 

 shallow umbrella are four purple horseshoe-shaped or circular 

 generative masses ; in the centre of the under surface is the 

 manubrium prolonged into four arms ; the margin of the umbrella 

 is provided with a fringe of very short fine tentacles, the uniformity 



Fig. 20. 



Carmarina hastata, one of the Trachomedusss. (After Haeckel, and from Encyc. 

 Britannica.) 



of the fringe being broken by eight notches, each containing 



a tentaculo-cyst ; each of the latter (Fig. 21) is covered by a Case 3, 



pair of minute lappets, hence Medusae of this type were called ^pnght part. 



Covered-Eyed ; while those of the Hydromedusan type, being 



without lappets, were called Naked-Eyed. 



The thickness of the umbrella is traversed by a system of simple 

 and branched canals, which pass from the central stomach to a 

 circular cnual running round the margin of the umbrella, Pro- 



