

MUSEUM OF COMPARATIVE ZOOLOGY. 265 



take origin from the base of the polypite, near its union with the peduncle. 

 The axis is large, muscular, and spirally coiled.* The color of its wall is yellow 

 and orange. The float is in no respects peculiar, and bears around the opening 

 by which the air-sac communicates with the surrounding water a number of 

 regularly arranged pigment-spots. The nectocalyces are arranged in many 

 rows, opening laterally in spirals on all sides of the animal. The most distally 

 placed bells from the float are the oldest, as in other Physophores. Directly 

 under the float there is a small cluster (it) of undeveloped swimming-bells. 

 Each nectocalyx has a cubical form, the flat faces of which conform to the 

 surfaces of adjoining bells. -The bell has in other particulars a great resem- 

 blance to the nectocalyx of other Physophores, and does not seem to differ 

 from that of Forslcalia contorta. The course of the radial tubes is like that in 

 Agalma. At the union of the radial tube with the ring canal on the bell 

 margin, there is a large yellow spot, which is an ocellus or sense organ of the 

 same kind as similar bodies in certain hydroid medusa 1 . On either side of it, 

 there is a short papilla of unknown function. In the undeveloped nectocalyx 

 we find a single large yellow spot of this kind, which forms a very conspicuous 

 body on the bell margin. Later in the growth of the nectocalyx, its compara- 

 tively large size diminishes. We should expect, if anywhere among the Physo- 

 phores, a development of the sense organs in Stephanomia. Its motion through 

 the water is so rapid that organs of this kind are necessary. Ocelli on the margin 

 of the nectocalyx are, however, not peculiar to Stephanomia. In our common 

 Diphyes similar ocelli are found, three in number, on the margin of the anterior 

 nectocalyx. The attachment of the covering-scales to the base of the polypites 

 and the distal end of the peduncle imparts to the polyx stem of Stephanomia 

 a diameter relatively greater than that of other Physophores. In Agalma the 

 covering-scales spring from the base of the polypite, of which the peduncle is 

 very short. In Stephanomia, however, the pedicle, which bears the feeding- 

 polyp, is so long that the covering-scale seems to hang from a point midway 

 between the axis of the animal and the mouth of the polypite. The tastern do 

 not difl'er from the tastern of other Physophores, except that they have long 

 peduncles, as is the case also with the polypites. 



The male and female bells arise from the same tastern at their junction with 

 their peduncles. The colony is monoecious. The sexual lulls resemble closely 

 those of Agalmnpsis graeile, sp. nov. In its motion through the water it is one 

 of the most active of all the Physophores. The combination of so many series 

 of nectocalyces can propel it in almost any direction witli the greatest ease, 

 whereas in Agalma and some others these propelling organs are obviously 

 placed in a disadvantageous position for quick movement. As it passes 

 through the water in the line of its axis, it sometimes combines a rotation of 

 the stem with the direct forward motion. 



When the colony is quiet in the water the peduncles of the polypites and the 

 organs which they bear are widely extended, 80 that its diameter is very great 

 as compared with its length. As the colony begins to advance in the line of 

 * In the same way as Forskalia contorta. 



