1897.] MR. E. T. BROWNE 0:^ BRITISH MEDUS.i:. 831 



the younger ones vary between 114 and 180. In the smallest 

 specimen the generative cells are just beginning to make their 

 appearance along some of the radial canals. The generative cells 

 are situated in the wall of the canal, and as they develop in size 

 the wall of the canal extends downwards, so that in the largest 

 specimens the wall hangs down as a large fold, about 4 mm. wide, 

 and of a purplish colour. The generative cells extend from the 

 stomach nearly to the ring-canal, terminating in the largest speci- 

 mens about 2 to 3 mm. from the margin. In this short portion 

 the canal is very broad, several times broader than the parts 

 bearing the gonads. 



Haeckel states that Polycanna fungina has alternating sterile 

 and fertile radial canals. The Valencia specimens have generative 

 cells on almost every canal, occasionally a sterile canal occurs in 

 one or two places on the umbrella. As the canals are of different 

 ages of growth, so are the generative cells, and consequently the 

 generative folds vary in size. 



Strethill Wright was successful in rearing the ova of Polycanna 

 vitrina (Gosse), and showed that an alternation of generations 

 existed, but the hydroids died at too early a stage for a satis- 

 factory determination of their generic position. 



The Tentacles and Marginal Vesicles, 



The smallest specimen shows that the medusa probably starts its 

 free-swimming life with four tentacles, and later on has eight and 

 then sixteen, which correspond to the perradial, interraclial, and 

 adradial sets, as in Phialidium. After sixteen are present the 

 tentacles develop in an irregular manner until the maximum 

 number, which is not yet known, has been reached. The largest 

 of the Valencia specimens has 56 tentacles and about 150 marginal 

 bulbs ; if the latter develop tentacles, a full-grown specimen would 

 have about 200 tentacles. The first appearance of a tentacle is 

 marked by a very small bulb upon the margin of the umbrella, 

 and the bulb grows to a considerable size before the tentacle begins 

 to grow out from it. The bulbs increase in number as the 

 umbrella increases in size, and consequently, in the later stages, 

 the bulbs and tentacles show various stages in development. A 

 bulb carrying a full-grown tentacle is very large and marked 

 externally with four or more longitudinal ridges. As the wall 

 of the bulb is very thin, there is a large internal cavity which 

 communicates with the ring-canal through a narrow opening. 

 The bulbs and the tentacles are of a light purplish colour. The 

 arrangement of the tentacles on the margin of the umbrella does 

 not coincide with the arrangement of the radial canals. 



The marginal vesicles are exceedingly numerous and irregular in 

 position ; there are usually two vesicles between every two marginal 

 bulbs, and the number varies between one and three. Each 

 vesicle usually contains four otoliths, but the nianber varies 

 from two to six. The arrangement of the otoliths inside the 



