100 THE ROYAL SOCIETY OF CANADA 
bulbs develop for the sixth series but apparently none of them get 
far enough to develop tentacles although some of them may get far 
enough to have the lithocysts develop at the base. The mouth 
remains sixteen-lobed but each lobe becomes serrated so that at times 
these cannot be made out readily. Some of the indentations may 
be deep enough to give the appearance of extra lobes but even in such 
cases the number of lobes so formed is never more than half the num- 
ber of the radial canals. The diameter of the stomach varies from one- 
half to one-third the diameter of the umbrella. 
The gonads begin to develop along some of the larger radial 
canals about the time the fifth series is nearing completion but the 
development is not rapid. Until the medusa reaches a diameter 
of about 60 mm. they are not very noticeable. They appear on all 
of the radial canals and become bi-lamellar. 
The excretory pores are not very noticeable in the early stages 
of development but by the time the tentacle bulb is large enough 
to develop a tentacle the excretory pore is distinctly evident. In 
the adult there is usually a pore to each developed tentacle bulb 
and occasionally on the large bulbs there may be two pores present. 
SUMMARY. 
After the first three series of radial canals are developed in the 
medusa, Æquorea, there is liable to be much irregularity but the de- 
velopment follows a definite plan more or less closely. The first 
series consists of four perradials; the second, four interradials; the 
third, eight primary adradials; the fourth, sixteen secondary adradials, 
of which the first eight are adjacent to the perradials, the second 
eight adjacent to the interradials; the fifth, thirty-two tertiary 
adradials, of which the first eight are adjacent to the perradials, the 
second eight adjacent to the interradials and the remaining sixteen 
adjacent to the primary adradials. The sixth series seldom becomes 
complete but the development as far as it goes occurs in the same order 
as the fifth series. 
The tentacles follow the same order as the radial canals. In 
general the rudiment of the tentacle bulb appears before the beginning 
of the corresponding radial canal. By the time the canal reaches the 
circumference the bulb is quite large but the tentacle has not started to 
develop and may not appear for some time after. While the bulb 
is quite small a lithocyst develops at one side of the base and shortly 
afterwards the one on the other side, or they may appear simul- 
taneously. There are thus two lithocysts to each well developed 
tentacle bulb. 
