REPRODUCTION, VEGETABLE (VEGETAHLE OVUM). 



256 



APPENDIX. On the relations which exist 

 between the animal and vegetable kingdoms, 

 as regards the function of reproduction. In 

 the introduction to the foregoing article, it 

 was observed that, if any analogies in deve- 

 lopment may be supposed to exist between 

 plants and animals, they are to be sought be- 

 tween the lowest members of the two series. 

 Whether we conclude that it is or is not pos- 

 sible to mark out the limit which separates 

 the one kingdom from the other, it is not to be 

 overlooked that the phenomena of reproduc- 

 tion, and consequently the whole circle of the 

 development, of the zoosporous Algae resem- 

 ble more those which present themselves on 

 the other side of the disputed territory, than 

 those which occur among the higher plants. 

 Let us compare the development of a unicel- 

 lular Alga, with that of one of the simplest 

 Infusoria. An egg-shaped body composed of 

 a homogeneous and contractile substance 

 as regards its chemical constitution nitroge- 

 nous displays active motions, and exhibits 

 two locomotive organs springing from its 

 smaller end. Soon, however, its motions be- 

 come languid ; a newly formed cellulose mem- 

 brane, which is not contractile, encloses it, 

 and now it undergoes a kind of cleavage, 

 which results in the formation of a number of 

 new bodies. In each of these, as soon as they 

 escape from the parent, the same transforma- 

 tion is repeated. 



In the other case, taking the development 

 of Vorticella as an illustration (in the de- 

 scription of which we follow Stein*), we find 

 that a disc-shaped mass of homogeneous con- 

 tractile substance (a monad), is transformed 

 into a stalked and ciliated Vorticella. After 

 Laving been for a time endowed with ac- 

 tive motion, and with a power of ingesting 

 food, the Vorticella enters into a state of re- 

 pose, and at the same time is enclosed in ti 

 flexible membrane or cyst. The interior of 

 the cyst is now occupied by a mass of proto- 

 plasma, which is no longer contractile, and 

 presents no trace of the structure of the 

 former Vorticella. By a process similar to 

 that which occurs in the plant, this plasma 

 divides into a number of disc-shaped bodies, 

 resembling that from which the parent origi- 

 nated. 



Between the Protozoon and the Protophy- 

 ton, there is an intermediate group, of which 

 the Euglena viridis, alluded to in $ 1., may be 

 considered as the representative. The Eu- 

 glena after actively moving for a time, enters 

 into the condition of repose, becoming at the 

 same time enclosed in a new membrane. What 

 follows this change, however, has not been as 

 yet ascertained. 



* Stein, Wiegmann's Archiv. fur Naturgesch. 

 1849. Bd. i. p. 92. 



The phenomenon of conjugation, also, while 

 it is without parallel among the higher plants, 

 presents itself under nearly similar conditions 

 among the Infusoria. According to the ob- 

 servations of Stein, the circle of changes 

 described in the preceding paragraph, is not 

 the only one by which in Vorticella the spe- 

 cific form is reproduced. A Vorticella enters 

 into a state of rest, and becomes encysted ; 

 it is not now, however, converted into a mass 

 of homogeneous protoplasms as in the former 

 case. The cyst membrane changes into a thin 

 walled vesicle, while from the body of the 

 enclosed Vorticella, which has assumed a 

 spherical form, there emanate a number of 

 contractile radiating processes. It is now a 

 Protozoon, identical with that to which has 

 been given the name Actinophrys. Now in 

 Actinophrys, the occurrence of conjugation 

 has been recorded by several trustworthy 

 observers. It was first described by Kol- 

 liker*, afterwards by Siebold f , and finally 

 by Colin. According to the last-mentioned 

 author, two neighbouring individuals after 

 approaching more and more closely to each 

 other, emit from their opposite surfaces, vesi- 

 cular processes, which finally unite. As the 

 union becomes more complete, the two seem 

 to form but a single animal. As to what are 

 the results of this remarkable conjugation, 

 neither Colin, nor, as far as we know, any 

 other observer, is able as yet to speak posi- 

 tively. Every fully formed Actinophrys ex- 

 hibits embedded in its substance a central 

 nucleus-like body ; this nucleus, according to 

 Stein, is sooner or later transformed into an 

 egg-shaped animal, which grows at the expense 

 of the parent, and finally becomes endowed 

 with active motion. At the smaller end is 

 formed a crown of cilia, at the larger an oral 

 depression, and soon there presents itself a 

 perfect Vorticella. It is, at least, extremely 

 probable that this development is the result 

 of the previous conjugation of two Actino- 

 phries. 



The analogies which have been under our 

 consideration in the preceding paragraphs, 

 may be placed in a clearer point of view, by 

 exhibiting them in a tabular form. Referring 

 the reader to the description contained in 

 $18. of the most simple form of unicellular 

 conjugating Algae (Palmogloea macrococca), 

 we shall contrast the circle of development, 

 as it presents itself in Palmogloea and Proto- 

 coccus on the one hand, with that of Vorti- 

 cella on the other, as follows : 



* Das Sonnenthierchen. Zeitschrift fur Wiss. 

 Zool. i. p. 198. 



f Ueber die Conjugation des Diplozoon para- 

 doxum, u. s. w. he. cit.ul. p. 62. 1851. 



J Heitrage zur Entwick. der Iiifusorien, /. c. iv. 

 p. 252. 



