The Life-history of Melicertidium octo- 
costatum (Sars), a Leptomedusan with 
a theca-less Hydroid Stage. 
By 
Prof. James F. Gemmill, University College, Dundee. 
With Plate 16. 
CONTENTS. 
PAGE 
DEVELOPMENT OF EaGs oF MELICERTIDIUM . ; . . 340 
DESCRIPTION OF THE TANK HybDrRoIp . , : ; : . o4l 
GENERAL . , : - ; : ; 2 i : . 344 
REFERENCES. : : t : é : . 346 
Tris well-known medusa (fig. 19) is classified among the 
Thaumantiadae, and is characterized by the presence of 
eight ‘radial’ canals on which the gonads are developed. 
The marginal tentacles are numerous (up to 140) and of 
unequal size, larger and smaller ones alternating more or less 
regularly. There are no lithocysts, cordyli or ectodermal 
ocelli. The manubrium is short, the mouth four-angled and 
without oral tentacles. The medusa has a fairly wide distribu- 
tion in the North-east Atlantic ranging from Bergen to 
Falmouth. (See EK. T. Browne, 4, for details and a discussion 
of the nomenclature.) The hydroid, as I have ascertained by 
rearing the eggs, proves to be a hitherto undescribed species 
identical with one which has been noted for several years 
(with a year’s interval of absence) growing abundantly and 
spontaneously in the tanks at the Millport Biological Station. 
An allied form Melicertum campanula (Agassiz) 
occurs in West Atlantic Canadian and U.S. waters. In 1863 
NO. 259 Aa 
