and the Elements in which they live. 157 



a heterogeneous group belonging to diiFereut types of the animal 

 kingdom; and that most of them, far from being perfect animals, 

 are only germs in an early state of development. The family of 

 Vorticellce exhibits so close a relation with the Bryozoa, and 

 especially with the genus Pedicellina, that I have no doubt that 

 wherever Bryozoa should be placed Vorticella should follow, and 

 be ranked in the same division with them. 



The last group of Infusoria, Bursaria, Paramecium and the like, 

 are, as I have satisfied myself by direct investigation, germs of 

 freshwater worms, some of which I have seen hatched from eggs 

 of Planaria laid under my eyes. This being the case, we see that, 

 without exception, the whole class of so-called Infusoria must be 

 dissolved into its various elements and divided partly among the 

 Articulata, and partly among Mollusca in the widest extension of 

 those groups (if it can be shown that Bryozoa belongs also to the 

 type of ]\Iollusca), that large numbers of them belong to the ve- 

 getable kingdom, and others are simply germs of other types, and 

 that no single one of them belongs to the type of Radiata. 



If we next consider the Polypi, we find them constituting an- 

 other main group and most natural class, to which indeed some 

 heterogeneous types have been annexed : upon the removal of 

 these however that class constitutes a very natural division of 

 the type of Radiata, among which they form the lowest class. 

 The natural groups which require to be removed from Polypi 

 are, — first, the so-called Hydroid Polypi, which, though truly 

 radiated animals, do not belong to this class, but are, as I have 

 shown from their structure, and as might long ago have been 

 inferred from their development, true members of the class of 

 Medusse, among which they constitute a type of stalk animals, as 

 crinoids among star-fishes*. 



The Bryozoa also are not constructed upon the plan of Radiata, 

 as has long been shown by ]\Iilne-Edwards and others. Their 

 true position is among Mollusca, and embryonic investigations 

 upon Ascidia have satisfied me that Bryozoa, compound, and 

 simple Ascidia, form a natural series of well-connected types lead- 

 ing to the true Acephala among ordinary Mollusca, among which 

 Bryozoa will form a natural group of compound animals, bearing 

 the same relation to the ordinary bivalve shells that common 

 corals bear to the simple Actiniai and Fungise. Though the 

 doubts entertained about the Foraminifera among Bryozoa would 

 not affect at all the points under discussion, I may as well state 



* See my paper upon the homologies of radiated animals with reference 

 to the classification of the so-called hytlroid polypi, read heibre the Ame- 

 rican Association for the Advancement of Science, held in Cambridge, Au- 

 gust 1849; also my lectures upon comparative embryology, delivered be- 

 fore the Lowell Institute, Dec. 18-lH. and Jan. lH4i». 



