58 REPORT ON THE PENNATULIDA. 



We would therefore suggest that the fracture at the lower end is 

 caused at the time of capture, and is due partly to the brittleness of 

 the stem, and partly to the firm implanting of the stalk in the sea 

 bottom. The usual site of the fracture — at the junction of rachis and 

 stalk (vitle Fig. 1) — strongly supports this view, for while on the one 

 hand the dredge dragging along the bottom would snap off the stem 

 exactly at this point, on the other the tangles brushing against the 

 rachis higher up would bend and break it at the very same spot, i.e., 

 its point of emergence from the ground. Knowing as we do that 

 Virpularia when living undisturbed not only has the stalk, which is 

 wanting in almost all dredged specimens, but also that the stalk is buried 

 completely in the sea bottom, this part of the explanation seems to us 

 entirely satisfactory. 



Concerning the fracture of the upper end, however, the case is 

 different. The cause here must be an altogether different and inde- 

 pendent one. It is almost inconceivable that any influence at the time 

 of capture could invariably break off the tops of the specimens. Neither 

 the dredge, nor the rope, nor the tangles, could, so far as we can see, possibly 

 effect this fracture : their tendency would always be, as we have just 

 shown, to break the stem at its point of emergence from the ground. 

 We are, thei-efore, driven to the conclusion that the upper fracture is 

 not effected at the time of capture, but that Virfiularia, while living 

 undisturbed at the bottom of the sea, has already lost its top. This is 

 confirmed by an observation of Darwin,* who describes the Virgularia 

 (Stylatula Danclnil of Kolliker) seen by him living on the shores of 

 Patagonia as truncated at the upper end. 



Having thus narrowed our problem and defined its limits more 

 precisely, we have now to determine, if possible, what are the causes 

 which, acting normally during the life of a Virgularia, and quite 

 independently of any influence exerted by man, lead to the almost 

 invariable truncation of its upper end. 



The first explanation that suggested itself to us was, that in the 

 ordinary course of growth the top, after attaining its full development, 

 dies, withers up, and drops off, and in this way causes the truncation. 

 This is at first sight an attractive theory, and accords well with the fact 

 that the leaves at the bottom of the stalk are always small and 

 immature, and gradually increase in size and development as we pass 

 upwards ; i.e., that the development of leaves appears to proceed from 

 below upwards. 



However, closer examination reveals fatal objections to this view. 

 In the first place the actual upper ends of the specimens as dredged, 

 show no sign whatever of disease, or of being about to perish. On 

 the contrary, in all the specimens examined the rachis is perfectly 

 healthy right up to the top. Secondly, the truncation does not occur 

 always at or about the same spot in different specimens, but at 



'■ Darwin : " Naturalist's Voyage Bound the World," 1860, p. 99. 



