98 THE ROYAL SOCIETY OF CANADA 
but unless some suitable colonies appear accidentally it may be long 
enough before the first stage in the medusa development can be de- 
scribed. 
When the medusa has four perradial canals, or canals of the first 
series, and four interradial canals, or canals of the second series, 
complete to the circumference, there are at the same time eight ten- 
tacles, four perradial, being well developed and the other four just be- 
ginning, but slightly past the bulb stage. Besides these there are the 
rudiments of eight other bulbs. There are eight lithocysts well de- 
veloped, one at each side of each perradial tentacle bulb, and’ eight 
others in process of development in a corresponding position relative 
to the interradial bulbs. The mouth is distinctly four-lipped. 
By the time the four interradial canals are complete, the be- 
ginnings of some or all of the adradial canals, or canals of the third 
series, may generally be seen. The eight tentacles are now well de- 
veloped. Eight tentacle bulbs, corresponding to the eight primary 
adradials, have grown much larger and eight more bulbs are beginning, 
one between each perradial and its nearest adradial. The second 
set of eight lithocysts is now quite distinct but there is no sign of any 
for the adradial bulbs. The mouth is still four-lipped. 
When the medusa has reached a diameter of 7 mm. the primary 
adradial canals are complete to the circumference and the secondary 
adradials, or canals of the fourth series, have started to develop. 
The first of them appear between the perradials and the adradials 
and these may be of considerable length before those between the 
interradials and the adradials make a start. The adradial tentacle 
bulbs are all supplied with tentacles, the bulbs between the perradials 
and adradials have increased in size but have not yet developed ten- 
tacles and the bulbs between the interradials and the adradials are 
visible but still small. As the adradial tentacles are developed, 
a pair of lithocysts, one at each side of the base, become apparent 
but none are yet visible for the next set of developing bulbs. The 
mouth has now become octagonal instead of four-lipped, as each 
lobe has now become distinctly notched. 
A 10-mm. medusa may have all of the canals of the fourth series 
complete but before the last of them reach the circumference, the next 
series of canals, the fifth, has started. The first canals of the fifth 
series appear between the perradials and the secondary adradials 
adjacent to them. The tentacle bulbs of the fourth series have not 
developed tentacles although those nearest the perradials are of 
large size, those next to the interradials being somewhat less so, 
while those for the fifth series nearest the perradials are just beginning 
to show. Each of the tentacle bulbs of the fourth series is now 
