186 Professor Owen on the Generation of the 



form of long chains, sometimes branched, sometimes expanding to form 

 a spherical bag, as in the well-known Volvox globator, which was long 

 deemed a single individual of a peculiar species. New spherical groups 

 of Voh'oces are thrown off into the interior of the parent monadiary, 

 which is rent open to allow them to escape. 



Another mode of generation is by gemmation or the development of 

 buds, which in some species, as Cheroma, grow out of the fore part of 

 the body, and in others, as Vorticdla, from the hind part near the stem, 

 or from the stem itself, from which the young animal soon detaches it- 

 self. In most Vorticcllidcej as in Carchcsuon and Epistylis, the small libe- 

 rated end of the body opposite the mouth is provided with a circle of 

 vibratile cilia, so long as the individual swims freely ; but these disap- 

 pear when the pedicle is developed. 



With regard to the more common fissiparous mode, Ehrenberg has 

 figured gradations of this spontaneous division of the organised contents 

 of the integument in the Oonium and Chlamydomonas, which may be 

 compared with the earliest stages of the development of the germ, as 

 figured by Siebold in the Strongylus sm^ Medusa, by Baer in the frog, and 

 by Barry in the rabbit. Dr Martin Barry, who has discovered the very 

 remarkable and complicated nature of this process in the mammalian 

 ovum, was alone perhaps in the condition to fully comprehend and ex- 

 plain its analogy to the fissiparous generation of the Polygastria, to 

 which, in 1840, I briefly alluded ; and this he has done in a paper, re- 

 plete with interesting generalizations, lately read before the Royal So- 

 ciety. I have been favoured by that indefatigable observer with the fol- 

 lowing notes of his ideas on this subject. 



" Between the appearance presented by the mammiferous germ during 

 the passage of the ovum through the Fallopian tube, and those met with 

 in the young Volvox globater while within the parent, I find a resem- 

 blance which is very remarkable indeed, extending even to minute de- 

 tails. Not only do the cells of which the young Volvox is composed 

 form a body resembling a mulberry, with a pellucid centre, but the 

 cells gradually increase in number, apparently by doubling, at the same 

 time diminishing in size, like the cells of the mammiferous germ ; which 

 they resemble also in being originally elliptical and flat. 



*' Some of the points of resemblance now mentioned were recognised 

 in the delineation of the Volvox given by professor Ehrenberg ; others 

 were noticed during some observations I have myself made on this very 

 interesting microscopic object. Professor Ehrenberg has figured five 

 pellucid globules in a young Volvox just escaped from the parent. 

 These, the germs of another set, evidently resulted from division of the 

 pellucid mass visible in another state : so that here is to be recognised 

 fissiparous generation of the kind I have described as reproducing cells. 



*' On examining the figures given by Ehrenberg of successive genera- 

 tions of the Chlamj^domonas, I see a resemblance to the two, four, eight, 

 &c. groups of cells in the mammiferous ovum too striking, not to sug- 



