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PROCEEDINGS OF THE [[April, 1857. 



In the same way we should not shut our eyes to the fact that 

 Lesson's genera Ratis and Acies are both very small, and their 

 characters make it not improbable that they represent different 

 stages in the growth of Porpita. 



PORPITA. Lamarck. 



So few have been the observations on the medusa-buds of 

 Porpita, that we cannot proceed to give 'a generic diagnosis of 

 them. Kolliker mentions that they are like the un-freed buds of 

 Velella. I can from my own observations confirm this so far as 

 agreement between the figures of the Velella-buds, given by 

 Kolliker, and the buds I have seen upon the following Porpita 

 are concerned. But I have never seen a Velella. The following 

 were the principal characters of the bud at the highest stage of 

 development which has come under my observation. The gen- 

 eral form was pyramidal, the vertex corresponding to the attached 

 extremity. The opening of the vail was, as far as could be as- 

 certained, not yet formed. There were no tentacula, but the four 

 points of the margin corresponding to the extremities of the ra- 

 diate tubes, were prominent and armed each with a few thread- 

 cells. The outline of the cavity to be expected within was not 

 traced out with such clearness as to enable me to assert its existence 

 from actual observation, but the arrangement of the parts within 

 can hardly be consistent with any other supposition. Near the apex 

 of the pyramid at the top of the bell-cavity was a lump of small 

 dark cells semicircular when viewed in profile, but quadrate like 

 the digestive trunks of most Hydroid medusae when viewed from 

 above, from which proceeded downward four lines, evidently the 

 radiate tubes. These were of a whitish color, like that of ground 

 glass, near the rudimentary digestive cavity, and this color became 

 confounded below with a reddish orange-colored enlargement of 

 the canal, showing that the perfectly developed medusa probably 

 has something like a colored marginal bulb. They were large 

 enough in nearly all the specimens to be brought, all the four 

 quite close together, and I did not observe with certainty the circu- 

 lar tube, even in one or two specimens in which these bulbs were 

 unusually separated. A character like one of Chrysomitra must 

 be noted. In the neighborhood of the lower colored extremities of 

 the radiate tubes were a number of scattered circular golden- 

 colored cells, on the inner surface of the yet unopened bell-cavity 

 which leads me to conclude that in the adult condition the bell- 



