Transactions of The Royal Society of Canada 
SECTION IV 

SERIES III DECEMBER 1916 NO Tego 

On the Development of Æquorea Forskalea. 
By C. MCLEAN FRASER. 
(Read May Meeting, 1916). 
During the months of April and May specimens of the medusa, 
Æquorea forskalea Peron et Le Sueur, in various stages of develop- 
ment are found in large numbers in Departure Bay and in the neigh- 
boring waters. By getting a large series of them it has been possible 
to trace the order of development of the radial canals, tentacles, 
lithocysts, excretory pores and lip folds. 
The youngest medusa yet obtained had four perradial canals com- 
plete to the circumference and four interradial canals started. The 
medusa was about 2 mm. in diameter. What size it is when it is 
liberated or how far development is gone at that time it is impossible 
to say, although but little time must have elapsed in the interval. 
If the Campanulina reported from this region is really the hydroid of 
Æquorea, and there is no reason to doubt it as no other Campanulina 
has been found near by, it may be some time before the gap will be 
filled. Since it was first reported from the San Juan Archipelago,} 
it was found on some small green alge, near Round island, Dodds Nar- 
rows, on June 18, 1913,2 and not again until April 5, 1916, in a location 
where one should scarcely expect to find a hydroid of any kind, viz., 
on the walking legs of the commensal crab, Pinnixa, taken from the 
mantle cavity of a horse clam, Schizotherus nuttalli. It was not 
alone however, as there were small specimens of Clytia edwardsi 
growing on the same crab. The specimens found here were at much 
the same stage as the previous specimens, showing no signs of develop- 
ing medusa-buds. As no specimen yet found had attained a height 
of 1 mm. it can readily be seen that it is a hopeless task to proceed 
to look for others as it would be a difficult matter to find them even 
if one knew where to look. The hydroids that produce these medusæ 
must be very plentiful as the medusæ appear in such large numbers 
1 West Coast Hydroids, 1911, p. 43. 
? Hydroids of the Vancouver Island Region, 1914, p. 157. 

Sec. IV, Sig. 1 
