336 HYDROIDiE. Part IV. 



breeze is fresh and the animal is driven before the wind, these tentacles are 

 stretched to a most extraordinary length, varying, according to circumstance, from 

 twenty to thirty, forty, and even fifty feet, and forming as many anchors upon 

 which it rides, without being cast adrift. I have observed them in stormy weather 

 struggling in that way against the elements, in order to avoid being thrown 

 ashore. It is curious to see how, inider these circumstances, they change their 

 position, by raising the pointed end of their air-bag and throwing themselves 

 suddenly upon the opposite side ; but I have never seen them emptying their 

 bag and sinking under the surface of the water. These large hydrae form small 

 bunches of two, three, or four, budding from a common hollow stem, which com- 

 municates with the chymiferous cavity extending between the inner and outer 

 wall of the air-bag. (PI. XXV. Fig. 3.) Bunches of similar hydras in larger num- 

 bers, but of a uniformly smaller size, alternate with these and occupy a position 

 on their lee. All these hydrce have nothing to do with nourishing the colony, 

 and their actinal end is closed; they are, evidently, simply locomotive individuals. 

 When the whole colony is at rest, they hang down loosely. 



The feeding hydras are also of two kinds, large and small ones, and, like the 

 locomotive hydrse, their difference of size seems to be primitive, and not the con- 

 sequence of a more or less advanced development. These individuals never have 

 tentacles; but they are clustered in bunches, budding in greater or smaller num- 

 bers from a common hollow stem, and, like the preceding, communicate with the 

 chymiferous cavity. All these bunches of feeding hydrJB are scattered along the 

 lee-side of the floating bag. (PI. XXV. Fig. 2.) I have seen them gorged with 

 food almost to bursting, but I have never seen undigested food in any other 

 kind of individuals. Neither the locomotive, nor the feeding hydras, ever produce 

 medusae-buds. These always arise from a third class of very small hydras, form- 

 ing very large clusters, suspended between the clusters of feeding hydrtE. These 

 prolific hydrJB resemble the locomotive hydraj most in general form, but, like 

 the nutritive hydrae, they are destitute of tentacles. The medusai-buds themselves, 

 of which there are males and females, arise singly, either from the base of the 

 prolific hydras or from the stems and branches which unite the latter. These 

 medusaj-buds are very similar to those of Tubularia proper, and Avither without 

 dropping from their parent stock. As soon as it is understood that the Pliysali^e 

 are compound communities, and not single individuals with very diversified organs, 

 the idea is at once suggested that the floating air-bag must be a large primary 

 hydra, assuming the special function of a floating apparatus, and the observations 

 of Huxley upon very young Physalia3 fully supports this view. I must abstain 

 from further details, from want of room, but shall resume my communications, upon 

 this subject, on another occasion. 



