OVUM. 



Some recent observations appear to throw 

 additional light on this subject, and to make 

 it probable that in some circumstances this 

 process is in some sort analogous, or at least 

 equivalent, to one of sexual reproduction. 



The first accurate observation of the de- 

 velopment of a progeny of young cells within 

 the body of a polygastrian was communicated 

 by Focke in 1844 to the meeting of natu- 

 ralists at Bremen, and the fact of the pro- 

 duction of internal germs or bodies resembling 

 ova or spores within the body of these ani- 

 malcules has recently received full confir- 

 mation from the observations of Stein and 

 of Cohn.* 



In Cohn's observations, which were made 

 on a parauiaecian polygastrian, the Loxodes 



Fig. 4. 





formation and extrusion of ova or germs in Loxodes 

 lursaria {from Cohn). 



a, animalcule, containing two young; b, contain- 

 ing six ; c, one of the embryos escaping ; d, e, two 

 ciliated embryos. 



bursaria, which is usually multiplied like the 

 rest, in the fissiparous mode, sometimes by 

 longitudinal, at others, by transverse division, 

 it was found that at certain periods there 

 were formed within the bodies finely granular 

 colourless cells, in some only one, more fre- 

 quently several, and occasionally as many as 

 six or seven, nearly of a uniform size, and 



ferred to under the head of ' sporiferous reproduction,' 

 by Prof. Rymer Jones, in the article POLYGASTIUA. 

 * Stein, "Untersuch. lib. die Entwick. der Infuso- 

 rien, Wiegmann's Archiv., 1849, vol. 1. p. 134. in 

 Ac-tinophrys, Acineta, and Chilodon uncinatus. 

 Cohn, in Zeitsch. fiir Wissensch. Zoologie, Xov. 

 1851, p. -2-J-. 



each presenting two contractile vesicles like 

 the parent. The escape of these bodies, by 

 their passage through an aperture temporarily 

 formed in the wall of the infusorian, was 

 carefully observed ; the exit of each embryo 

 occupied about twenty minutes. Soon after 

 their escape they exhibited active ciliary mo- 

 tion, and moved about with all the appearance 

 of embryo-infusoria. Although the farther 

 development of these bodies was not traced, 

 the observations on this animal, and on an- 

 other, the Urostyla grandis, afford sufficient 

 proof that the infusoria may be propagated by 

 minute separate germs, as well as by division 

 of their bodies. 



A similar production, but more numerous, 

 of an internal progeny, has been observed in 

 the microscopic parasitic animalcule termed 

 Gregarina, which infests the intestinal canal 

 of a number of insects, earth worms and some 

 other invertebrate animals.* 



The simple Gregarina consists of a single 

 cell filled with granular substance, and con- 

 taining a distinct nucleus. It has no intestinal 

 canal, nor other internal organisation ; is gene- 

 rally of an elongated shape, and creeps about by 

 motions of slow contraction of its substance. 

 The formation of the progeny or smaller 

 bodies within the Gregarina is attended with 

 a remarkable change in the parent animal, 

 which has been carefully observed by Stein. 

 This change, in which the animal appears 

 double for a time, had been previously no- 

 ticed by Kolliker and others, and had been 

 interpreted by Kolliker as the conversion of 

 a single animal into two, by a process analo- 



-F/g. 5. 



GregarnuE {from Kolliker.) 



a, single; 6, c, d, united ; e,f, g, the formation of 

 the navicella-like progeny ; h, three of these ua- 

 viceliae (from Stein). 



* These animals were first accurately described 

 by Leon Dufour in 1837 (Ann. des Sc. Xat. vol. vii. 

 p* 10.). They have since been studied with great 



B 4 



