8 



OVUM. 



gous to transverse fission. Stein, on the 

 other hand, has been convinced by a very at- 

 tentive observation of the different stages of 

 this process, that it is of an opposite character, 

 and that, previous to the development of the 

 young progeny, two of the Gregarinae have 

 become fused, or united into one. As the 

 two are about to unite, they gradually change 

 their form from that of elongated planaria- 

 like animalcules, to that nearly of hemispheres, 

 closely pressed together; then a complete 

 fusion or union occurs, and the whole of the 

 granules of both having become amalgamated 

 in one sphere, the development of the internal 

 progeny takes place gradually from the mass. 

 This progeny consists in a vast multitude 

 of minute bodies, shaped like the Navicellae 

 (among the Diatomacea3), but different from 

 these bodies, and very probably constituting 

 the reproductive germs or embryos of Gre- 

 garina?. The development of this Navi- 

 cella-like progeny into the Gregarina does 

 not appear as yet to have been traced ; as in 

 this animal, like many other parasites, the 

 progeny is required to migrate during its de- 

 velopment from one stage to another, and the 

 little bodies are passed out of the alimentary 

 canal of the insect before undergoing farther 

 changes. 



The views and observations of Stein, how- 

 ever, should they be confirmed by others, 

 would prove the very remarkable fact, that 

 the phenomenon of conjugation, or fusion of 

 two unicellular individuals, hitherto supposed 

 to be confined to some of the simpler plants, 

 as Closterium, Spirogyra and Zygnema, &c., 

 may occur also in animals of a similar simple 

 structure. 



These observations on the Gregarina are 

 not altogether of an isolated kind. In a 

 recent interesting notice of this subject by V. 

 Siebold *, he has called attention to the ob- 

 servation of Kolliker on the conjugation or 

 fusion of two individuals of Actinophrys -|-, a 

 spherical infusorian animalcule analogous to 

 the Amoeba or Rhizopoda, by its slowly con- 

 tractile, amorphous texture, and its long, ra- 

 diating, contractile processes. Kolliker ob- 

 served two individuals of this animalcule to 

 approach each other, adhere, and gradually to 

 fuse into one, which soon assumed the same 

 globular form, with the radiated contractile 

 processes, as each of the two that formed it, 

 and differing only from them by the increase 



success by various observers, as V. Siebold (Beitrag. 

 Z. Naturgesch. Wirbellos. Thieve, 1839, p. 63.). 

 Henle (Mailer's Archiv, 184.5, p. 3(59.), and Stein in 

 the same, 1848, p. 182. Kolliker (Zeitsch. f. Wiss. 

 Zool. 1848 and 1849), and as many as eighty dif- 

 ferent, species of them have now been discovered. 



* Zeitsch. f. Wissensch. Zool. March, 1851, 

 p. 62. 



f Op. cit. 1849, p. 207. In this very interesting 

 memoir Kolliker has proved the animal nature of 

 the Actinophrys by his observations on its contrac- 

 tility, and on the manner in which the particles of 

 solid matters, vegetable and animal, are involved in 

 its substance for the purpose of digestion, and their 

 remains again rejected when that process is com- 

 pleted. 



of size which it sustained. This very curious 

 observation has been confirmed by Stein, in 

 an allied genus Podophyra, both of the sessile 

 and pecliculated kind ; and V. Siebold has ob- 

 served the same phenomenon in a species of 

 Acineta belonging to the same family of 

 Infusoria. Cohn, also, has repeated and con- 

 firmed Koiliker's observations in the Acti- 

 nophrys sol, and has made a farther discovery 

 of great interest in connection with the pro- 

 cess of conjugation in these animals, having 

 observed after the union, both in the Acineta 

 and Actinophrys, the development, at certain 

 periods, between the united individuals, of a 

 spherical body of considerable size, vesicular 

 form, and containing within it a nuclear forma- 

 tion of variable magnitude. 



Although the farther development of this 

 body has not yet been traced, it seems not 

 improbable to V. Siebold that it may be 

 analogous to the reproductive capsule or 

 sporo-cyst of the conjugating Closterium or 

 Zygnema*, from which bodies it seems to be 

 certain that a number of reproductive spores 

 are produced. 



Since the foregoing was written, indeed, 

 renewed researches by Stein -j- have come 

 under my notice which are confirmatory of 

 the view previously stated as to the repro- 

 ductive process in Gregarina, and explain in 

 a great degree the apparently incomplete 

 observations of Pineauj and others as to the 

 varying conditions of Vorticella, and also 

 extend our knowledge of the production of 

 germs of the Infusoria. Stein observed the 

 Vorticella microstoma to lose its pedicle, 

 become free, assume the globular form, and 

 at last to be enclosed in a cyst produced by 

 exudation from its own body. After a time 

 the band-like nucleus of the encysted Vorti- 

 cella is divided into a number of small discoid 

 bodies, not by a regular or progressive process 

 of cell-cleavage, but at once and directly. 

 These minute bodies gradually increase in 

 size at the expense of the granular and fluid 

 substance surrounding them in the cyst, and 

 ultimately escape in the form exactly of Monas 

 colpoda (of Ehrenberg). These very soon fix 

 themselves ; and a fine pedicle is developed at 

 the place of attachment. In other instances 

 the Vorticella-cyst was observed to send 

 forth long contractile processes from its sur- 

 face, and then assumed very much the form 

 and appearance of an Acineta or Actinophrys; 

 and in this case a new Vorticella was formed 

 in the interior in the manner of a bud. The 

 Vorticella, therefore, it would appear, is ca- 

 pable of reproduction in two modes, by the 

 development of embryoes from the divided 

 nucleus, which Stein on this account proposes 

 to call nucleus germinativus (the testis of 

 Ehrenberg) j and by gemmation from an 

 intermediate Acineta form. The first form 

 Stein would regard as the equivalent of sex- 



* See the Article VEGETABLE OVUM for an ac- 

 count of this process in the lower forms of plants, 

 t Zeitsch. fur Wissensch. Zool. Feb. 1852. 

 Ann. dcs Scicn. Nat. 1845 and 1848. 



