REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



257 



Zoosporous Unicellular Alga. 



Production of a series of 

 Zoospores. 



Cessation of motion. 



Conjugating Unicellular Alga. 



Production of a series of sterile 

 Podophrija:. 



Conjugation of two Podophryaj. 

 Cessation of growth. 



Protozoon.* 



Production of a series 

 Monads, 



which are transformed into Vor- 

 ticella;. 



Cessation of motion. 



Transformation'of Vorticella; into 

 sexual Actinophries. 



Conjugation followed by 



Cessation of growth. 



* In the zoosporous Algne, constantly recurring series of unisexual generations are produced indefinitely. 

 In Vorticella the production of Monads may also recur repeated!}', without the intervention of any 

 sexual stage. So long as this is the case the two developments correspond completely. 



Here it may be observed that in the stage 

 of cessation of growth, which, in the Pro- 

 tozoon, as well as in the Protophyton, follows 

 the act of conjugation, we have a condition 

 which corresponds to that of the ovum of 

 the higher animals. The ovum after passing 

 through a period of repose, resembling that 

 which presents itself in Podophrya, exhibits 

 a series of transformations, which correspond 

 to the later steps of the developments under 

 our consideration. This correspondence is, 

 as might be expected, more distinctly seen in 

 the lower than in the higher animals. Thus 

 for example, in the development of a Trema- 

 tode Worm (Distomum pacificum), the mass 

 of the yolk is transformed into a locomo- 

 tive rudiment resembling an infusory animal. 

 Within this originates an asexual, but fertile 

 nurse, the homologue of the Vorticella, in the 

 interior of which is formed a second and 

 numerous generation of animals endowed 

 with locomotion (Cercariae). In these, after 

 a time, the locomotive power is lost, and each 

 finally becomes a sexual Distomum.* 



Although the foregoing homologies are 

 founded on observations the details of which 

 are as yet imperfectly worked out (on which 

 account it may seem somewhat premature to 

 draw attention to them), they are not open to 

 the objections which may be urged to homo- 

 logies supposed to exist between the highest 

 members of the two series. There, the con- 

 necting links are wanting; here, we pass 

 through closely related intermediate forms, 

 from the Alga to the Protozoon, and from 

 the Protozoon to the Trematode Worm. 

 Hence, while we are not justified in applying 

 the term ovum to the generative product of 

 the phanerogamous plant, the present state 

 of our knowledge allows us with propriety 

 to compare with the ovum the result of con- 

 jugation as it occurs among the Algae. 



The differences in chemical composition 

 which exist between the Alga? and the Pro- 

 tozoa will not serve as a ground of distinc- 

 tion. Euglena is invested during its period 

 of repose with a cellulose membrane and 

 contains granules of chlorophylle. In Poly- 

 toma uvella we find, on the one hand, the 

 contractile vesicles of the infusory animal, 

 on the other, starch in the granular form, 

 so characteristic of the plant.| 



(.7. Burdon Sanderson.) 



* Cams, " System der Thierischen Morph.," s. 329. 

 f A. Schneider, " Beitriige zur Entwick. der In- 

 Supp. 



BIBLIOGRAPHY. ALG.E. Kohlreuter, Das en- 

 deckte Geheimniss der Cryptogamie. Carlsruhe, 

 1777. Hedwig, Theoria Generationis et Fructifica- 

 tionis Plant. Crypt. Leipsic., 1798. Voucher, His- 

 toire des Conferves d'Eau douce. Geneva, 1803. 

 Kaidfiiss, Die Keimung der Characeen. Leipsic, 

 1825. Unger, Die Pflauze im Momente der Thier- 

 werdung. Vienna, 1843. Midler (A'.), Entwick. 

 der Chara, Bot. Zeit., 1845, p. 410. Ralfs, British 

 Desmidise. London, 1848. Kiitzing, Phycologia 

 generalis. Nordhausen, 1845. 



FUNGI AND LICHENS. Malplghi, De Plantis 

 quas in aliis vegetant, Op. omu. t. i. 48. Meyen, 

 Prlanzen-Physiologie, v. iii. Meyer, Entwick. der 

 Flechten. Gbttingen, 1825. Walhotlt, Natur- 

 gesch. der Flechten. Frankfurt, 1825. Unger, Die 

 Exantheme der Pflanzen. Vienna, 1838. Korber, 

 DeGonidiisLichenum. Berlin, 183!). Schmitz,'Bei- 

 trilge zur Anatomic und Physiologic der Schwamme. 

 Linnrca, 1843. 



HEPATIC^E AND MOSSES. SchmideJ, Icones 

 Plantarum, 1762. Hedwig, Fundamenta Hist. Nat. 

 Muse. Frond. Leipsic, 1782. Nees v. Esenbeck, 

 Naturgesch. der Europ. Lebermoose, 1838. Bi- 

 sc/wjf and Lindenberg, Nova Acta A. L. C., xvii. and 

 xviii. Mold, Anatom. Untersuch iiber Sphagnum, 

 Sporangien der mit Gefassen versehenen Ciyptog. 

 Tubingen, 1837. Schimper, Recherches sur les 

 Mousses. Strasbourg, 1848. Lanzius Beninga, De 

 Evol. Sporidiorum. Gb'ttingen, 1844. 



FERNS AND EQUISETACE^E. Agardh, and Vou- 

 cher, Mem. du Mus. d'Hist. Nat. de Geneve, 1822- 

 23. Kaulfuss, Das Wesen der Farnnkrauter. Leip- 

 sic, 1827. Moll, Morphol. Betrachtungen iiber die 

 Cryptog., Tubingen, 1837. Bischoff, Entwick. der 

 Equisetaceen, Nova Acta A. L/C., xiv., 1828. 

 Ncigeli, Anther, der Farnnkrauter, Zeit. f. w. Bot,, 

 i. 1G8. Zurich, 1844. Leszczyc Suminski, Ent- 

 wick. der Farnnkrauter. Berlin, 1848. Merklin, 

 Prothal. der Farnnkrauter. St. Petersburg, 1850. 



RlIIZOCAKPE^E AND LYCOPODIACE.E. BtSCkoff, 



in op. cit. N'dgeli, in op. cit., extr. in Ann. des Sc. 

 Nat., ix. 99. Milde, Entwick. der Equiseten und 

 Rhizocarpeen, Nova Acta A. L. C., 1852. 



PHANEROGAMIA. Camerarius, Dissertatio de re 

 Botanica, 1676. 4to. Tubingte, 1717. Grew, Anat. 

 of Vegetables, &c., 8vo. London, 1672. Malpighi, 

 Anatome Plantarum. Op. omnia, t. ii., fol. Lon- 

 don, 1687. Linnieus, On the Sexes of Plants. Lon- 

 don, 1786. Morland ( Samuel"), Observations on the 

 Parts and Use of the Flower and Plant, Phil. Trans., 

 1703, p. 1477. Treviranus, Die Entwick. des Em- 

 bryo. Berlin, 1815. Amid, Mem. della Soc. Ital., 

 xix., pp. 253-257. Padua, 1823. Brown (Robt.), Bo- 

 tanical Appendix to King's Voyage. London, 1826. 

 Fritsche, Devel. du Pollen, Me'm. de 1'Acad. de St. 

 Petersbourg, 1835. Schacht, Entwickelungsges- 

 chichte des Pflanzcn-Embryo. Amsterdam, 1850. 



The reader is further referred to various researches 

 contained in the 3rd Series of the Ann. des Sc. Nat. 



fusorien," Muller's Archiv. No. 2. 1854. These re- 

 searches we recommend to the reader's attention, 

 as containing observations of great importance in. 

 relation to the present question. 



S 



