Chap. VIII. SIPHONOPHOR.E IN GENERAL. 335 



forth, with a proboscis, four radiating chA-miferous tubes, and a circular tube. These 

 fertile Medusae are either scattered between the secondary hydras, or gathered in 

 bunches. 



4. Diphya3 C«^'. — Compound community of combined twins, arising from an 

 egg-born Medusa. The community consists of twin sterile Medusa^, withoi°t tentacles 

 or proboscis (Ersaja or Aglaisma, when young), from which arise a string of com- 

 pound, heteromorphous twins, one of wliich is a hydra, the other a fertile medusa, 

 either male or female, without tentacles but with proboscis, becoming free together 

 (Eudoxia or Cuboides). 



SECTION II. 



THE GENUS PHYSALIA, AND OUK PHYSALIA ARETHUSA. 



Although for many years past I have had ample opportunities of investigatino- 

 the North American Siphonophora^ this volume has already attained dimension^, 

 which forbid that I should dwell upon them for the present. I will, therefore, 

 hmit myself to a few remarks upon one of their most remarkable representatives! 

 from which the mode of combination of the heterogeneous individuals, forming 

 this kind of communities, may best be appreciated. By far the most prominen°t 

 part of the compound body is a large, oblong, pear-shaped bag, full of air, of a 

 bright, bluish tint, varying to rose-color, floating lightly upon the surfxce of the 

 ocean, so that it is altogether raised above the level of the water. An elegant, 

 comb-like, crenulated crest, edged with a rose-colored rim, and traversed by^sim- 

 ilar bands, forms a sort of sail above the float, from the lower surface of which 

 hangs a most extraordinary variety of appendages, appearing, at first sight, like 

 bunches of varied tentacles. These appendages are all clustered upon one and 

 the same side of the air-bag, and crowded toward its broader end, while the 

 tapering end has none of them. A more careful inspection readily discloses the 

 heterogeneous nature of these appendages, some of which are simple, elongated 

 hydr*, with or without tentacles, and others medusa-buds. Unless we compare these 

 hydraj among themselves, and ascertain their mode of combination, we can have only 

 a very imperfect idea of their extraordinary diversity. In the first place, it sliould 

 be noticed that the largest hjdrve are all arranged along the windward side of 

 the animal, and that they are provided with the longest and most complicated 

 tentacles. (PI. XXXV. ^>. 1.) As I have seen these Physalia by thousands, in 

 every kind of weather, I have noticed that they always present the same side 

 to the wind, that is, the one from which hang the longest tentacles j and when the 



