198 L. Agassiz on the Natural Relations between 



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 Vorticellse 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 investiga- 

 tion, germs of fresh- water 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 ele- 

 ments and divided partly among the Articulata, and partly 

 among Mollusca in the widest extension of those groups (if 

 it can be shewn that Bryozoa belongs also to the type of 

 Mollusca), that large numbers of them belong to the vege- 

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

 and that no single one of them belongs to the type of Eadiata. 



If we next consider the Polypi, we find them constituting 

 another 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 shewn from their structure, 

 and as might long ago have been inferred from their develop- 

 ment, true members of the class 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 Ra- 

 diata, as has long been shewn by Milne Edwards, and others. 

 Their true position is among Mollusca, and embryonic inves- 



* See my paper upon the Homologies of Radiated Animals with reference to 

 the classification of the so-called Hydroid Polypi, read before the x\merican 

 Association for the Advancement of Science, held in Cambridge, August 1849; 

 also my lectures upon Comparative Embryology, delivered before the Lowell 

 Institute, December 1848 and January 1849. 



