334 GENERAL HISTORY OF THE INFUSORIA. 



as in Paramecium caudatum, but they are produced by a different mechanism. 

 Each of the two nuclei divides into two halves, as in the act of spontaneous 

 division ; and the four fragments thus produced form an equal number of 

 perfect ova. Lastly, in Sjjirostomum amhigimm, we have seen, in individuals 

 which have been copulating for some time, the forty or fifty grains of the 

 long flexuous cord which traverses the body become rounded and detached 

 from each other. But we have been unable to discover in these all the 

 characters of an ovum with the same distinctness as in the preceding species, 

 no doubt because they had not yet arrived at their complete development. 



" Y. I have not witnessed the deposition of the ova in these animals. It 

 is very probable that they escaped by the anus, or by some neighbouiing 

 apertiu'e. Thus, in the Stylonycliice, I have seen them collect in the posterior 

 part of the body, which bears the anal orifice, and diminish gradually in num- 

 ber from the fii'st or second day after the copulation. It is a singular thing, 

 that about this period a round pale body begins to make its appearance in the 

 centre of the animal ; this becomes constricted about the middle, and recon- 

 stitutes the double nucleus of Stylonycliia. 



^' VI. The Infusoria are destitute of copulatory organs. In most cases the 

 copulation is effected by simple juxtaposition, the two mouths establishing 

 the sexual communication {Paramecium, Bursaria, Euplotes, Chilodon, Sjjiro- 

 stomum). In the Oxytrichina the union is more intimate, and goes so far as 

 to constitute a true soldering of the two individuals for more than two-thirds 

 of their anterior part. Any one who had not witnessed all the phases of this 

 singular copulation, would be unable to avoid regarding this state as a longi- 

 tudinal division, proceeding from behind forwards, in a single animal. But, 

 even if direct observation were wanting, the concomitant changes of the 

 internal organs, which are so characteristic, cannot leave the least doubt as 

 to the actual signification of this act." 



Ovules. — In Ehrenberg's organology of Infusoria, ovules or ova assumed a 

 high importance. The structures he so designated had no distinctive featiu'es 

 assigned them, whereby they could be distinguished from other corpuscles 

 and granules in the interior ; and, in consequence, theii' existence could not 

 be confirmed by other microscopists, who for the most part declared that the 

 supposed ova were indifferently alimentary vacuoles, particles of food, fat 

 globules, or the ordinary granules of the interior. The general opinion became 

 pronounced against the very existence of ovules and of development by their 

 means, whilst the deposition of ova, which Ehrenberg believed he witnessed in 

 several instances, was explained to be an act of diffluence misconceived. This 

 explanation, for instance, has been given to his recorded observation and his 

 figures of the act of oviposition in Colpoda CucuUulus, which represented this 

 animalcule as bursting and giving vent to strings of ova, which first ran 

 together in a reticulate manner, and then, after a time, became individually 

 developed into young Colpodce. According to the opposite view, the bursting 

 and extrusion of contents are no other than the phenomena of diffluence and 

 the dispersion of particles of sarcode, whilst the young supposed to originate 

 from those particles are merely minute Monads or monadiform coi-puscles 

 found in company with the Colpodce. 



One objection brought against the assumption of ova being ejected from 

 Protozoa in the exercise of a generative function is certainly frivolous — viz. 

 that the empty or broken shells of the ova ought to be met with ; for the shell 

 of an e^g, however useful in larger animals as a defence against injuiy, is no 

 essential part of an ovum from which a new being can be developed. 



Although the existence of ova among the CiLiata has been denied by the 

 great authorities on Infusoria — by Kolliker, 8iebold, Leuckart, Cohn, Stein, 



