IN THE ANIMAL KINGDOM. 81 



never able to trace their farther progress, but he conjectured 

 that they -might give origin to Vorticella forms, to complete 

 the genetic cycle. It is possible this may be the destiny of 

 those acineta-embryos which M. d'Udekem has seen to be- 

 come encysted, but it is now clearly ascertained, both by 

 this observer and by J. Miiiler and Lachmann, that they 

 may also be directly developed again into fresh Acinetw* 



§ 3. REPRODUCTION IN THE COELENTERATA. 



Until of late the lowest of the four primary divisions of 

 the Animal Kingdom admitted by Cuvier — the Radiata — 

 remained much in the condition in which that illustrious 

 naturalist found the whole invertebrate series — a sort of 

 lumber store, in which all forms not readily reducible 

 under the three higher divisions were conveniently stowed 

 away. Even after the labours of later authors had extri- 

 cated from the confused assemblage various aberrant forms 

 of the Molluscous and Articulate types — as by associating 

 the Polyzoa with the Tunicata, the Lernseadaj with the 

 Crustacea, and the Entozoa with other vermiform tribes — 

 it still remained as impossible as ever to establish any com- 

 munity of organization among the residuary species. Later 

 researches have shown, however, that the restricted Radiata 

 fall into three groups, all equally natural, though of very 

 different relative value — namely, the Protozoa, which have 

 just been noticed, the Caelenterata and the Echinodermata. 

 Of these the two former are now ranked as primary divi- 

 sions, while the position of the last, which is evidently of a 

 subordinate character, still continues to be one of the great 

 puzzles of systematic zoology. 



The Coelenterata, as established by Leuckart and Frey, 

 coincide with the group termed NematojjJiora by Professor 



* Annals of Nat. Hist., 2d Ser., IX., 171, 3d Ser., IV., I. 



E 3 



