DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHIATE POLYPI. 389 
animals frequently united even in the same genus which have not a classical rela- 
tionship. 
But Renier and Savigny had already shown that the animals of Botryllus and 
Alcyonium, Linn., were not, as had been generally supposed, Polypes, but possessed 
a structure similar to that of Ascidia ; whilst the descriptions and figures given by 
various writers of some of the cortical Polypes showed that these were closely allied 
to Actinia. 
But though some of the larger forms had been thus more accurately investigated, 
the hundreds of minute species that remained must necessarily have escaped obser- 
vation, until the more general use of the microscope and the great improvements 
lately made in that instrument, opened up a wide and almost entirely new field of dis- 
covery, which the inefficient instruments of previous investigators had only just 
enabled them to enter upon. 
By this means the currents observed by Spallanzani to be produced by some of 
these animals, and attributed by him to the action of the arms, were shown by Stein- 
buch* * * § , by Fleming-}' in Valkeria, and by Grant^ in Flustra, to be due to the vibra- 
tion of cilia, by which the sides of the tentacula were fringed ; and to the last-men- 
tioned naturalist we are also indebted for many important observations on the ciliated 
reproductive gemmules of this family, on the form and growth of the cells, and on the 
digestive cavity. 
It was shortly after discovered by Milne Edwards and Audouin that some of 
these compound polypes possessed an anal as well as an oral opening to the alimentary 
canal ; a discovery which Edwards communicated to the Acad, des Sciences in 1828 §, 
and proposed thereupon to found a division of the class Polypes into different families, 
according to the forms of the alimentary canal. In this class, however, he also in- 
cludes Sponges. 
A similar discovery was also made about the same time by Ehrenberg, indepen- 
dently of that of Edwards, and was taken by him as the basis of his classification of 
Polypes ||, dividing these animals into two principal groups, Anthozoa and Bryozoa, 
according as the alimentary canal has one or two external openings; a division which 
he has since (1835) modified by separating the Sertularim and other hydriform Po- 
lypes, which form a third group denominated by him Dimorphsea. 
This type of structure, observed shortly after (in 1830) by Thompson^ in Ireland, 
* Analecten Neuer Beobachtungen und Untersuchungen fur die Naturkunde 1802, p. 89, quoted by 
Dr. Sharpey, Cycl. Anat. art. Cilia, p. 609. 
f Mem. of Wern, Soc. Fol. Part V. p. 488. 
+ Edinburgh New Philosophical Journal, vol. iii. 1827. 
§ Resume des Recherches sur les Animaux sans Vertebres, faites aux iles Chaussay, par MM. Audouin et 
Milne Edwards. Annales des Sciences Naturelles, t. 15. Sept. 1828; and Recherches Anatomiques, Phy- 
siologiques et Zoologiques sur les Eschares, par M. H. M. Edwards. Ib. t. 16. Juillet 1836. 
0 Symbolae Physicse. 
Zoological Researches and Illustrations, Memoir V. Cork, 1830. 
3 E 2 
