24 



ZOOLOOT. 



jelly-fish (Fig. 22). All jelly-fishes are more or less bell 

 or umbrella shaped, and lire delicate transparent creatures 

 which move about in the water, by opening and closing 

 the edge of the disk-like body. From the centre of the 

 body hangs down a hollow proboscis-like tube, the stom- 

 ach, from the base of which radiate four canals or passages 

 which open into a circular passage around 

 the edge of the disk. Tliis is the water-vas- 

 cular system, and the fluid it contains is sea- 

 water mixed with the digestive fluid; this 

 fluid thus rudely corresponds to the blood of 

 higher animals. Four long thread-like ten- 

 tacles in the Coryne hang down from the 

 edge of the disk. These delicate jelly-fishes 

 jiossess a nervous ring passing around the 

 edge of the disk, and also eyes and simple 

 ears (otoci/sfs) situated at intervals on the 

 edge of the disk. 



The medusae arise from little bud-like 

 swellings on the young or ITydroid (Fig. 

 21, a); these enlarge, and finally become 

 detached and swim about as at Fig. 23. 



Some Ilydroids like Serfiilaria (Fig. 23) 

 are encased in horn, and closely resemble 

 delicate sea-weeds. They are commonly 

 thrown upon sea-beaches. 



Our common large jelly-fish or "sun-fish" 

 so often thrown ashore on sandy beaches is 

 the Avrclia (Fig. 27). It grows eight or 

 ten inches in diameter. Its tougli, jelly-like 

 convex disk is smooth above, but hollowed 

 out beneath into a broad stomach witli a square mouth, 

 the edge of which is minutely fringed, bearing four fringed 

 broad, short tentacles. On the fringed margin are eioht 

 covered eyes situated in indentations, which divide tlie disk 

 into eight slightly m:irkcd lobes. Tlie four main water- 

 vascular canals subdivide as seen in Fig. 27, into numer- 



FlG. 22 — Free Me- 

 dusa of Coryne, 

 with tlie four 

 loiijc tentacles. 

 Knlarged. 



