24 
ZOOLOGT, 
jelly-fish (Fig. 22). All jelly-fishes are more or less bell 
or umbrella shaped, and are 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. This 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 
possess a nervous ring passing around the 
edge of the disk, and also eyes and simple 
ears (otocysfs) situated at intervals on the 
edge of the disk. 
The medusae arise from little bud-like 
swellings on the young or Ilydroid (Fig. 
21, a); these enlarge, and finally become 
detached and swim about as at Fig. 22. 
Some Hydroids like Sertularia (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 Aiirelia (Fig. 27). It grows eight or 
ten inches in diameter. Its tough, jelly-like 
convex disk is smooth above, but hollowed 
out beneath into a broad stomach with a square mouth, 
the edge of which is minutely fringed, bearing four fringed 
broad, short tentacles. On the fringed margin are eight 
covered eyes situated in indentations, which divide the disk 
into eight slightly marked lobes. The four main water- 
vascular canals subdivide, as seen in Fig. 27, into numer- 
FiG. 22 —Free Me- 
dusa of Coryne^ 
with the four 
long tentacles. 
Enlarged. 
