60 ZOOLOGY 
The generative glands are on the sub-umbrella surface of 
the radial canals. Limnocodium, the only freshwater medusa 
with whose anatomy we are acquainted, is placed by Lankester 
in this order. It forms an exception to the rule of the absence 
of a hydroid form. A small hydranth has been described 
as budding off the medusae, which are found at intervals in 
tanks of the Victoria regia in the Botanical Society’s Garden, 
vegent’s Park. 
Order 6. Narcomedusae. 
CHARACTERISTICS.—T7he Narcomedusae always have their ten- 
taculocysts free. The tentacles arise some way wp the aboral 
Jace of the umbrella, not from its edge. Their bases are con- 
nected with the edge of the umbrella by stiffening rods of tissue 
termed Peronia. These may also be found in the Tracho- 
medusae. 
The generative organs arise from the sub-umbrella surface 
of the stomach, not on the radial canals. 
Ciass B. SCYPHOMEDUSAE, 
CHARACTERISTICS.—The hydroid stage of this sub-class is a 
polype, which may give rise to the medusa, not by budding 
but by transverse fission. It is termed the Scyphistoma. The 
mouth of the Scyphistoma is squarish, and the coelenteron is 
sub-divided by four ridges, termed taeniolae, which project 
Jrom the sides into its lumen. 
The medusa has also a square mouth, whose angles may be 
produced into four oral processes. The edge of the wmbrella 
is lobed. The sense organs are modified tentacles, into the 
base of which the coelenteron is produced. No continuous 
nerve ring exists, but scattered nerve centres are found round 
the margin, and no true velum is present. CHARYBDAEA 
Jorms, however, an exception to this statement. The generative 
cells are endodermic in origin, and the medusae are unisexual. 
In the Scyphomedusae a primary series of four tentacles 
corresponding to the four angles of the mouth are the first to 
be formed. This affords a convenient method for mapping 
out the regions of the body. The radii on which they are 
