Chap. V. 



BOUGAINVILLIA SUPERCILIARIS. 



291 



Fig. 37. 



Fiy. 38. 



BudofBouGAiN- 



VILLIA SUPERCIL- 

 IARIS, Still con- 

 nected with its Hy- 

 droid. 



PI. XXVII. consists in showing the shght difference in their form. My son, how- 

 ever, has traced its further growth to its final development, and there is no 

 doubt left now, that the Hydroid described above is the parent stock of the 

 free medusa, described under the name of Hi^ipocrene superciliaris ^ in my Contri- 

 butions to the Natui-al History of the Acalephs of North America. 

 The young medusa, when about to separate from the hydroid 

 (wood-cut 37), is almost globular; it has a short digestive cavity, 

 terminating in four slight knobs, in the prolongation of the lines 

 of the chymiferous tubes, four pairs of tentacles, equalling in length 

 the diameter of the bell, with a 

 well-marked eye-siseck at the base 

 of each. The bulb at the base of 

 the tentacles is not yet well sepa- 

 rated fi'om the circular tube. But, 

 as the tentacles lengthen, which 

 takes place very rapidly, as soon as the medusas 

 have become detached, the swelling of the tentacles 

 appears more distinctly. The knobs at the four 

 corners of the digestive cavity assume more the 

 shape of a short branch. The general outline is 

 more hemispherical. The opening of the veil in- 

 creases, and the young medusa is a Bougainvillia 

 superciliaris, with but two tentacles, and the oral 

 bunches slightly developed (wood-cut 38), agreeing, 

 in this respect, entirely with the mode of growth 



of the young of Margelis,^ in which the oral bunches are still very little ramified, 

 even when there are as many as six tentacles at the base of 

 each chymiferous tube. The tentacles at the apex of the sensi- 

 tive bulb are first developed, smaller tentacles being added, simul- 

 taneously, on each side of the original pair. The adjoining 

 wood-cut, Fiff. 39, of an adult specimen, shows to what extent 

 the process goes on. For further details upon the full-grown 

 medusa, I refer to my former paper. 



Young BouGAis vii.i.iA surEHCiLiAEis, shortly 

 freed from its Hvdroid. 



Fig. 39. 



Adult Bougainvillia. 



' The name ITippoerene is now changed to Bou- 

 gainvillia, for the obvious reason that Montfort's 

 genus Hippocrene, among the Gasteropods, cannot 

 be discarded, as it has been by most Conchologists 

 of the present day. 



'^ Margelis is the name proposed by Steenstrup 

 for the European species of Bougainvillia, which, 

 as McCrady has first pointed out, are generically 

 distinct from the American species, and the latter 

 agrees with the Pacific type. 



