Dr. A. Braun on the Vegetable Individual. 369 



usual mode of reproduction to be understood in their true mean- 

 ing. It was attempted to reconcile them with the customary 

 mode by an unnatural interpretation, which regarded them as 

 subversive exceptions to the general rule ; while on the contrary 

 almost all later works ^' bring to light a multitude of unexpected 

 iacts which take their places naturally under the law of alter- 

 nation of generation as now known, and substantiate the perti- 

 nent words of Goethe with which Steenstrup opens his Memoir : 

 " Nature keeps on her course, and what seems an exception is in 

 rule/^ It was Sars, however, who first gave the answer to the 

 riddle, the key to the newly opened domain, when he said of the 

 course of development of Medusa j that here "it was not the in- 

 dividual, but the generation, which underwent the metamor- 

 phosis f.^' This was the true point of view ; for Steenstrup 

 dwelt too exclusively on the physiological side, the functional 

 relations, of the alternating generations. Steenstrup, in fact, 



I'Insectologie ' in 1745, though made in 1740, belong here. Also Cha- 

 misso's correct observations of alternation of generation in Salpa:, described 

 in his Memoir, De Animalibus quibusdam e classe Vermium Linnaiana, 

 Fasc. 1, 1819. Fragments in regard to the alternation of generation of 

 Trematoda were known (but as such they did seem very enigmatical) by 

 Bojanus's Beschreibung d. konigsgelben Wiirmer (the " nurses " of Tre- 

 matoda according to Steenstrup) aus welchen Cercarien (the larvae of the 

 final generation) herauskommen (Isis, 1818), and by von Bauer's important 

 work on Cercaria; and the related Bucephalus (Beitrage zur Kenntniss d. 

 niederen Thiere, Act. Nat. Cur. vol. xiii. 1827). 



* Of the later works, by which the field of alternation of generation has 

 been extended, I will adduce in particular : Sars, Fauna litoralis Norvegiae, 

 1846, in which the sections especially important in relation to alternation 

 of generation are those on Syncoryna, Podocoryna, Perigonimus, Cytais, 

 as well as on Agalmopsis, Diphyes, and Salpa. — Van Beneden, Recherches 

 sur I'Embryogenie des Tubulaires (1814) ; Mem. sur les Campanulaires de 

 h cote d'Osteiide (1845, in the Mem. de I'Acad. Roy. de Bruxelles, t. xvii.) ; 

 Recherches sur I'Anat., la Physiol, et le Devel. des Bryozoaires (Mem. de 

 I'Acad. Roy. de Br. t. xviii.). — Dujardin, Sur le Devel. des Mediises et des 

 Polypes hydraires (Ann. des Sc. Nat. Nov. 1845). — Krohn, Bemerkimgen 

 iiber die Geschlechtsverhaltnisse d. Sertularinen (in Miiller's Archiv, 1843, 

 p. 174); Ueber d. Fortpfl. u. Entw. der Biphoren (Froriep's neue Notizen, 

 No. 868, 1846). — Busch, Beob. iiber Anat. u. Entw. d. Infusorien (Arch, 

 f. Naturgesch. xv. p. 92). How great an importance must be attributed to 

 the discovery of alternation of generation in dispelling the darkness which 

 until then settled on the history of the life and development of Entozoa, 

 may be seen in particular in Siebold's pregnant communications in R. 

 "Wagner's Handworterbueh d. Physiologic, p. 640 (Article ; Parasiten). 



t Sars, I. c. p. 29. This assertion, of course, must not be understood as 

 if the particular generation did not come in for its part of a metamorphosis. 

 Sars' view is most beautifully corroborated by a comparison with })lants ; 

 as in plants the metamorphosis of the individual itself is connected with 

 the formation which leads to the completion of new parts, which in their 

 turn have their own subordinate metamorphosis. 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. xviii. 24 



