90 



ESSAY ON CLASSIFICATION. 



Part I. 



SECTION XX, 



ALTERNATE GENERATIONS. 



While some animals go on developing gradually from the first formation of their 

 germ to the natural end of their life, and bring forth generation after generation, a 

 progeny which runs with never varying regularity through the same course, there 

 are others which multiply in various ways, by division and by budding,^ or by a 

 strange succession of generations, differing one from the other, and not returning, by 

 a direct course, to their typical cycle. 



The facts which have led to the knowledge of the phenomena now generally 

 known under the name of alfenudc generation, were first observed by Chamisso and 

 Sars, and afterwards presented in a methodical connection by Steenstrup, in his 

 famous pamphlet on that subject.^ As a brief account of the facts may be found in 

 almost every text-book of Physiology, I need not repeat them here, but only refer 

 to the original investigations, in which all the details known upon this subject may 

 be found.^ These facts show, in the first place with regard to Hydroid Medusae, that 

 the individuals jjorn from eggs, may be entirely different from those Avhich produced 

 the eggs, and end their life without ever undergoing themselves such changes as 

 would transform them into individuals similar to their parents;* they show further. 



' Much information useful to the zoologist, may 

 be gathered from Braun's paper upon the Budding 

 of Plants, q. a,, p. 18, note 3. The process of multi- 

 plication by budding or by division, and that of sexual 

 reproduction, are too often confounded by zoologists, 

 and this confusion has already led to serious mis- 

 constructions of well known facts. 



" Steenstrup, (J.,) Ueber den Generationswech- 

 sel, q. a., p. 69, note 3. 



' See the works quoted above, page 69, note 3, 

 and p. 70, note 1, also Carus, (V.,) Zur niihern Kennt- 

 niss des Generationswechsels, Leipzig, 1849, 8vo. — 

 Einige Worte iiber Metamorphose und Generations- 

 wechsel, Zeitsch. f. wiss. Zool., 1851, vol. 3, p. 359. 

 — Owen, (R.,) On Parthenogenesis, or the Succes- 

 sive Production of Procreating Individuals from a 

 single Ovum, London, 1849, 8vo. — On Metamor- 

 phosis and Metagenesis, Ann. and Mag. Nat. Hist., 



2d ser. vol. 8, 1857, p. 59. — Prosch, (V.,) Om 

 Parthenogenesis og Generationsvexel et Bidrag til 

 GenerationsliBren, Kicibenhavn, 1851. — Leuckart, 

 (R.,) Ueber Metamorphose, ungeschlechtliche Ver- 

 mehrung, Generationswechsel, Zeitsch. f. wiss. Zool,, 

 vol. 3, 1851. — Dana, (J. D.,) On the Analogy 

 between the Mode of Reproduction in Plants and the 

 " Alternation of Generations " observed in some 

 Radiata, Amer. Journ. A. and Sc, 2d ser. vol. 10, 

 p. 341. — Ehrenberg, (C. G.,) Ueber die Formen- 

 bestixndigkeit und den Entwickelungskreis der orga- 

 nischen Formen, Monatsber. der Akad., Berlin, 1852, 

 8vo. 



* Polymorphism among individuals of the same 

 species is not limited to Acalephs ; it is also observed 

 among genuine Polyps, the Madrepores, for example, 

 and among Bryozoa, Ascidians, Worms, Crustacea 

 (Lupea), and even among Insects (Bees). 



