112 ESSAY ON CLASSIFICATION. 



There is still much diversity of opinion among natu- 

 ralists respecting the limits of Articulata ; some being 

 inclined to separate the Arthropods and Worms as dis- 

 tinct branches, while others unite them into one. I 

 confess I cannot see the ground for a distinction. The 

 worm-like nature of the larvre of the majority of Arthro- 

 pods and the perfect homology of these larvae with the 

 true Worms, seem to me to show beyond the possibility 

 of a doubt, that all these animals are built upon one and 

 the same plan, and belong, therefore, to one branch, which 

 contains only three classes, if the principles laid down in 

 my second chapter are at all correct, namely, the Worms, 

 Crustaceans, and Insects. As to the Protozoa, I have little 

 confidence in the views generally entertained respecting 

 their nature. Having satisfied myself that Colpoda and 

 Paramecium are the brood of Planarise, and Opalina that 

 of Distoma, I see no reason why the other Infusoria, in- 

 cluded in Ehrenberg's division Enterodela, 1 should not 

 also be the brood of the many lower Worms, the develop- 

 ment of which has hitherto escaped our attention. Again, 

 a comparison of the early stages of development of the 

 Entomostraca with Eotifera might be sufficient to show, 

 what Burmeister, Dana, and Leydig have proved in 

 another way, that Eotifera are genuine Crustacea, and not 

 Worms. The vegetable character of most of the Anen- 

 tera has been satisfactorily illustrated. I have not yet 

 been able to arrive at a definite result respecting the 



LEUCKART, (R.,) Zool. Unters. q. a. von Messina. Arch. Nat., 1857, I, p. 



STEENSTRUP, (J.,) Die Hectocotylen- 41. VAN DER HOEVEN, (J.,) Beitrag 



bildung bei Argonauta und Treinoc- zur Anatomic von Nautilus Pom- 



topus. erklart durch Beobachtung pilius L., besonders des Mannlichen 



iihnlicher Bildungen bei den Cepha- Thieres, Arch. f. Nat. 1857, I, page 



lopoden im Allgerneinen, Arch. Nat., 77. 



1856, I, p. 211. TROSCHEL, (F. H.,) 1 That the Vorticellidae are Bryo- 



Benierkungen uber die Cephalopoden zoa, has already been stated above. 



