ClIAl". I. 



METAMORrilOSES OF ANIMALS. 



VI 



iiH'iit. not only in tlio difll'vent orders of the class, bnt oven in different genera 

 of the same falTlil3^ The larvaj of many have a close resemblance to diminutive 

 Ctenophoraj, and may be homologized -with this type of Acalephs. 



As I shall hereafter refer frequently to the leading divisions of the animal king- 

 dom, I ought to state here, that I do not adopt some of the changes -which have 

 been proposed lately in the limitation of the classes, and Avliich seem to have been 

 pi-etty generally received with favor. The undivided type of Radiata appears to 

 me as one of the most natural branches of the animal kingdom, and I consider 

 its subdivision into Coelenterata and Echinodennata, as an exaggeration of the ana- 

 tomical differences observed between them. As for as the plan of tlioir structure 

 is concerned, they do not differ at all, and that structure is throughout homologi- 

 cal. In this branch I recognize only three classes, Pohjpi, Acakpluv, and EcIduoJcr- 

 mata. The chief difference between the two first lies in the radiating partitions of 

 the main cavity of the Polypi, supporting the reproductive organs; moreover, the 

 digestive cavity in this class consists of an inward fold of the upper aperture of 

 the common sac of the body, while in Acalephs there exist radiating tubes, at least 

 in the j)roks nmlusina, which extend to the margin of the body where they ana.s- 

 tomoze, and the digestive cavity is hollowed out of the gelatinous mass of the 

 body. This is equally true of the Hydroids, the MedusiB proper, and the Cteno- 

 phorse ; but nothing of the kind is observed among Polj'pi. Siphonophorse, whether 

 their jit'oles medusina becomes free or not, and Hydroids agree in having, in the proles 

 inedusina, simple radiating tubes, uniting into a single circidar tube aroimd the mar- 

 gin of the bell-shaped disk. These two groups, constitute together, one natural 

 order, in contradistinction from the Covered-eyed Medusae, whose radiating tubes 

 ramify towards the margin and fonn a comphcated net of anastomoses. Morpho- 

 logically, the proles poli/poidea of the Acalephs, is as completely an vAcaleph, as their 



Ak. (1. "Wiss., Berlin, 18.52. — Ueber don allge- 

 meincn Plan in dor Entwickelung d(?r Echiiiddt'rmen, 

 Ak. d. AViss., Berlin, 18.5;]. — Ufber die (tattiingen 

 der Seeigellarven, 7te Abli., Ak. d. "Wiss., 1855. — 

 Ueber den Canal in den Eicrn der Ilolotlnirien, 

 Miiller's Arcli., 18.54, p. GO. — French abstraels of 

 these papers may be fonnd in Ann. Sc. Nat., 3e 

 ser., 1852 and '53, vols. 17, 19, and 20; An English 

 account is published by Huxley, (Tu. H.,) Report 

 upon the Researches of Prof. Midler into the Anat- 

 omy and Development of the Eehinodcrms, Ann. and 

 Mag. Nat. Hist., 2d sen, vol. 8, 1851, p. 1. — Kokex 

 und D.VNiELSSEN in Nyt Magazin for Naturvid, vol. 5, 

 p. 253, Christiania, 1817 ; Ann. Sc. Nat. 1847, p. 347. 



— Agassiz, (L.,) Twelve Lectures, etc., p. 13. — 

 Derhes, (A..) Sur la formation de I'embryon chez 

 I'oursin comestible, Ann. Sc. Nat., 3e ser., vol. 8, 

 p. 80. — Bush, (W.,) Beobaehtungen, etc., q. a. — 

 Ueber die Larve der Comatula, Miiller's Arch. 1840, 

 p. 400. — Kuonx, (A.,) Ueber die Entwickelung der 

 Seesterne und Ilolothurien, Miiller's Ardi., 1853, 

 \i. 317. — Ueber die Entwickelung einer lebendig 

 gebiihrenden Ophiun-, Miiller's Arch., 1851, p. 338. 



— Ueber die Larve des pA'hinus brevispinosus, Miil- 

 ler's Arch., 1853, p. 3G1. — Beobachlungen iiber 

 Echinodcrmenlarven, Miiller's Arch., 1854, p. 208. — 

 ScHULTZE, (M.,) Ueber die Entwickelung von Ophio- 

 lepis sciuamata, Miiller's Arch., 1852, p. 37. 



