Page:The Zoologist, 1st series, vol 4 (1846).djvu/204

1370 fowl as well as other birds ; namely, that of being able to expel at pleasure the air within the various cavities of the body, and which, when the air-cells are filled with air, is the cause of the buoyancy and resistance to the water of the former class, and en- ables them to float without any effort or exertion to themselves, &c." And at the con- clusion of those observations in allusion to land-birds, 1 have further stated that "I apprehend that without this power of ejecting or getting rid of the buoyancy caused by the air within the body of all descriptions of birds, that a hawk or any other bird desirous of making a swoop or sudden downward descent would not be able to effect this object so easily, unless the internal air was first expelled in addition to the force derived from volition, which it also possesses. Mr. Atkinson was pleased afterwards to animadvert with considerable severity and at considerable length, upon my observa- tions as above stated, but to which I added no rejoinder, contenting myself with merely stating, some months afterwards, that I had since had an opportunity of watching for some time a moorhen, with all but its "head and neck and just the top of the back and tail completely under water," and that it kept itself in that position for a conside- derable time without the aid of any weeds for its feet, which I could all the time see, were not holding by anything whatever. But in the May number of the 'Zoologist,' Mr. Atkinson again renews his strictures on the subject, and quotes the following pas- sage, the substance of which he had inserted in a previous number of the 'Zoologist.' "And yet, (Zool. 1326) if he (Mr. S.) will turn to my paper (Zool. 757) he will observe that I have expressed myself thus : 'If then W.H.S. maintains that moorhens or any other birds can keep themselves in what I call a state of submergence, without the aid of weeds or flags, or other objects external to themselves ; I beg leave to differ from him, if he means only that the moorhen, together with various other birds, is ca- pable of maintaining itself in what I call a partially submerged state, I cordially agree with him." But how does this "cordial agreement" in any way bear out what Mr. Atkinson has before asserted to be the fact, (Zool. 498) namely, " that no moorhen — that no bird whatever indeed, could put itself into this posture and retain it indepen- dently of external assistance." But after Mr. Atkinson's admission, that we cordially agree, that the power necessary to keep a moorhen, (or any other bird) to use his own words, " in a partially submerged state," is not derived from its feet holding upon any weeds ; then I am the more puzzled to know, where the line is to be drawn, and at what particular depth such power is required ; supposing the head and all parts of the bird's body to be under water. There are to me, many other startling circumstances in Mr. Atkinson's last observations, which I am desired to consider, but which I think do not apply to the matter in question. There is, however, another point unconnected with the moorhen's feet ; namely, with reference to my "suggestions" only, as to birds expelling internal air, which I would wish to clear up, and in which I have been totally mistaken. I did not for a moment mean to state, nor do I think, taking the whole context of what I did say, there is anything which can possibly support the sup- position that I intended to maintain a moorhen or other aquatic bird, by merely eject- ing or letting off two or three puffs of internal air, and clearing its air-cells, would by that means alone acquire the power of going straight to the bottom of the water ; and to sink at pleasure, and without any other power to enable it to do so. I only meant to convey the idea by that "suggestion," that by expelling a certain portion of inter- nal air (for were it to expel all internal air it would also expel life itself) such expul- sion of air might aid and assist, and be an accelerating cause "in addition to the power derived from volition" to enable it to submerge itself. The term "hypothetical,"