80 



ESSAY ON CLASSIFICATION. 



Part I. 



embraces two groups, the Acari and the Arachnoids proper, corresponding respec- 

 tively in this class to the Entomostraca and the higher Crustacea. The embryo 

 of the Acari resembles somewhat that of the Entomostraca, whilst that of the true 

 Spiders^ recalls the metamorphosis of the higher Crustacea. On the ground of the 

 similarity of their young, some animals, formerly referred to the class of Worms,^ 

 are now considered as Arachnoids ; but the limits between the aquatic Mites and 

 the Pycnogonums are not yet quite defined. 



In the branch of Vertebrata, all classes have been extensively studied, and as 

 far as the principal types are concerned, the leading features of their develojjment 

 are satisfactorily known. Much, however, remains to be done to ascertain the minor 

 modifications characteristic of the different families. It may even be, that further 

 investigations will greatly modify the general classification of the whole branch. 

 The class of Fishes^ may require subdivision, since tlie development of the Plagios- 



lotalpa vulgaris.) Muller's Archiv, 1844, p. 27. — 

 KuLLiKER, (A.,) Observationes de prima Insecto- 

 rum Genesi, Turiei, 1842, 4to. fig. — Zaddach, (G.,) 

 Die Entwickelung ties Pliryganiden Eies, Berlin, 

 1 vol. 4to. 1854. — Leuckardt, (R..) Ueber die 

 Micropyle und den feinern Bau der Schalenliaut bei 

 den Insekteneiern, Miiller's Arch., 1855, p. 90. — 

 Newport, (Geo.,) On the Organs of Reproduction 

 and the Development of Myriapoda, Phil. Trans. R. 

 Soc, 1842, II. p. 99. — Stein, (Fr.,) Vergeiehende 

 Anatomic und Physiologie der Insecten, Iste Monogr., 

 Die weibliehen Geschlechtsorgane der Kiifer, Berlin, 



1847, fol. fig. — SiEBOLD, (C. Tii. E. v.,) Ueber die 

 Fortpfianzung von Psyche, Zeitsch. f. wiss. Zoo!., 



1848, vol. 1, p. 93. — Leydig, (Fr.,) Einige Remer- 

 kungen iiber die Entwickelung der Blattliiuse, Zeitseh. 

 f. wiss. Zool., 1850, vol. 2, p. C.2. — Meyer, (II.,) 

 Ueber die Entwickelung des Fettkorpers, der Tra- 

 cheen und der keimbereitenden Geschechtstheile bei 

 den Lepidopteren, Zeitsch. f. wiss. Zool., 1849, vol. 1. 

 — Burnett, (W. J.,) Researches on the Develop- 

 ment of viviparous Aphides, Amer. Journ. Sci. and 

 Arts, 1854, vol. 17, p. 62 and 261. — As far as the 

 metamorphoses of Insects, after the eclosion of the 

 larva, are concerned, I must refer to the works of 

 Eeaumer and Roesel already quoted, and to almost 

 eveiy modern book upon Entomology. The meta- 

 morphoses of North American Insects are minutely 

 described in Harris's Report, q. a. 



* Herold, (M.,) De generatione Aranearum in 

 ovo, Marburgi, 1824, fol. fig. — Ratiike, (II.,) 

 Ueber die Entwickelung des Scorpions; Zur Mor- 

 phologic, q. a. — VanBeneden, (P.J.,) Recherches 

 sur ITIistoire naturelle et le developpenient de I'Atax 

 ypsilophora, M^ni. Ac. Brux., 1850, vol. 24, p. 444. 

 — Wittich, (W. II. v.,) Observationes quaedani de 

 aranearum ex ovo evolutione, Diss, inaug. Halis 

 Sax., 1845. — Die Entstehung des Arachnideneies 

 im Eierstoek, Muller's Arch., 1849, p. 113. — Carus, 

 (.J. V.,) Ueber die Entwickelung des Spinneneies, 

 Zeitsch. f. wiss. Zool., 1850, vol. 2, p. 97. — Dujar- 

 DiN, (F..) Memoire sur des Acariens sans bouches, 

 dent on a fait le genere llypopus et qui sont le 

 premier age des Gamaoses, Ann. Sc. Nat., 1849, 

 vol. 12, p. 243 et 259. 



^ Kaufmann, (Jos.,) Ueber die Entwickelung 

 und zoologische Stellung der Tardigraden, Zeitsch. 

 f. wiss. Zool. 1851, vol. 3, p. 220. — VanBeneden, 

 (P. J.,) Recherches sur I'organisation et le develop- 

 penient des Linguatules (Pentastoma.) Mem. Ac. 

 Brux. vol. 15, I., p. 188. — Schubert, (T. D.,) 

 Ueber Entwickelung von Pentastomum ttenioides 

 Zeitsch. f. wiss. Zool. 1852, vol. 4, p. 117. — Wil- 

 son, (E.,) Researches into the Structure and De- 

 velopment of a newly discovered Parasitic Animal- 

 cule of the Human Skin, Phil. Trans. R. Soc. 1844, 

 p. 305. 



' FoRCHHAMMER, (G.,) De Blcnnii vivipari 



