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. Miiller and Laehmann, that they 

 may also be directly developed again into fresh Acineta?.* 



3. REPRODUCTION IN THE (XELENTERATA. 



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 Lernseadae 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 Ccelenterata 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 Nematophora by Professor 



* Annals of Nat. Hist., 2d Ser., IX., 471, 3d Ser., IV., 1. 



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