384 Mr, Hogg's Observations on the Spongilla fluviatilis, 



than either to the locomotive gemmules of Zoophytes, or to the Volvoces* 

 themselves, we may justly conclude that the sporules of the Sponges are of a 

 vegetable nature. 



Furthermore, I consider that those hairlike, vibratory, and minute append- 

 ages called cilia, as instruments of locomotion, acting somewhat after the 

 ■ manner of little oars or fins, are peculiar to animals and to animal substances, 

 and that they never can exist upon any vegetable f production whatever. 

 Grant, Dalyell, Farre, Johnston, and others, describe the gemmules of Zoo- 

 phytes as being furnished with these cilia, and that by them alone they are 

 impelled through the water. The body of the f^olvox globator is likewise 

 covered with similar organs according to Professor Ehrenberg, who has be- 

 sides discovered that the cilia of the Infusoria have extremely small muscles 

 attached to their roots, by which the vibratory motions are performed. Those 

 naturalists, then, who reason solely from analogy, would, from the similar 

 movements of the sporules of the Ectosperma and Sponges, at once decide that 

 all those sporules move by the same means by which the Infusorians and the 

 gemmules of the Zoophytes do, and consequently, that they have such cilia. 

 But here analogy is of no assistance : for these organs of locomotion have 

 never yet been discovered on any vegetable body, although sought for with the 

 aid of very powerful magnifiers. M. Donn6 very recently, in endeavouring to 

 ascertain the cause of the circulation in the Chara, pressed out from a tube of 

 the Chara hispida a great number of granules ; amongst these were seen some 

 which had a rotatory movement, more or less rapid, independent of the 

 movement of general circulation : some turned round on themselves without 

 changing place : others were carried along by the current, but still preserving 

 their spontaneous rotatory movement. He supposed that they possessed cilia 

 as organs of their motions, but records, " I examined if there existed vibra- 



* Recent microscopic examinations of some of the Infusoria, (among others) of Monas lens, Kolpoda 

 cucullus, Brachionus ovalis, &c. have shown to me, that in addition to the characteristic distinctions 

 pointed out in the text, these animalcula plainly differ from the locomotive sporules of the Spongilla 

 by their great restlessness, and by their being almost constantly engaged in searching for, or hunting 

 after, their food or prey. — J. H., Feb. 12, 1839. 



t Of course, I need scarcely observe, those fine hairs or fringes, which are named cilia by botanists, 

 and occurring on different vegetable substances, are perfectly distinct. 



