22 
Tank No. 20. 
jelly-fish, however, the stalk is short and divided into a number of small 
lappets, each of which bears a mouth leading into a common cavity, the 
stomach. From the edge of the umbrella hang down long tentacles, which 
the animal can at will contract and elongate to a considerable extent. 
These tentacles are provided with numerous stinging-cells, such as have 
been described in the case of the Actiniae (see p. 15); and, as there, they 
afford an efficient means of defence for the delicate body. The unpleasant 
Fig. 18. Rhizostoma pulmo, Fig. 19. Cotylorhiza bor- Fig. 20. Pelagia noctiluca, 
small specimen. bonica, V 2 nat. size. Ya nat. size. 
Fig. 21. Tima Jlavilabris, 
1/2 nat. & ize. 
Y 2 nat. size. 
stings experienced occasionally in sea-bathing are generally due to contact 
with these jelly-fish. Some species, indeed, which attain a size of one to 
two feet and a weight of 50 to 60 pounds, produce very dangerous stings. 
A few species shine at night with a greenish light; thus Pelagia 
has received the specific name of noctiluca ("night-lantern”; not to be 
confounded with the much humbler organism, which has Noctiluca for 
its first name). — Some species of fish spend the early part of their 
life under the protection of the umbrella of Rhizostoma and Cotylorhiza, 
and even eat away parts of the medusae. 
