CILIATA 777 



several elongated cavities, arranged in a radiating manner, so 

 as to give to the whole somewhat of a star-like aspect, and 

 the liquid contents are seen to be propelled from the former into 

 the latter, and vice versa. Further, in Stentor, a complicated net- 

 work of canals, apparently in connection with the contractile 

 vesicles, has been detected in the substance of the ' ectosarc,' and 

 traces of this may be observed in other Infusoria. In some of the 

 larger animalcules it may be distinctly seen that the contractile 

 vesicles have permanent valvular orifices opening outwards, and that 

 an expulsion of fluid from the>body into the water around it is 

 effected by their contraction ; in some vorticellids the contractile 

 vesicle is connected by a canal with the ' vestibule ' which lies beneath 

 the mouth opening, and when the vesicle contracts the water is driven 

 into the mouth, and so to the exterior. Hence it appears likely that 

 their function is of a respiratory and depuratory nature ; and that they 

 serve, like the gill-openings of fishes, for the expulsion of water 

 which has been taken in by the mouth, and which has traversed the 

 interior of the body. 



Of the reproduction of the ciliated Infusoria our knowledge 

 though imperfect has advanced. As has been well said by Mr. 

 Adam Sedgwick, 1 'the more decent work of Biitschli and Maupas 

 [has] shown that in their reproduction these animals resemble other 

 Protozoa ; that is to say, that the whole body participates in the 

 reproductive fission, that the parent disappears in the offspring, and 

 that special conjugating cells of the nature of ova and spermatozoa are 

 not formed. Maupas 2 especially, by following the history of the 

 individual resulting from conjugation, has definitely established the 

 fundamental distinction between conjugation and reproduction, and 

 has thrown a flood of light upon the meaning of the whole phenomenon 

 of conjugation.' The best evidence is that of Gruber, which will be 

 mentioned directly. Binary subdivision would seem to be universal 

 among them, and has in many instances been observed (as elsewhere) 

 to commence in the nucleus. The division takes place in some species 

 longitudinally, that is, in the direction of the greatest length of the body 

 (fig. 593, D, E, F), in other species transversely (fig. 597, C, D) ; while 

 in some, as in Chilodon cucullulus (fig. 595), it has been supposed to 

 occur in either direction indifferently. But it may fairly be questioned 

 whether, in this last case, one set of the apparent ' fissions ' is not 

 really ' conjugation ' of two individuals. This duplication is per- 

 formed with such rapidity, under favourable circumstances, that, 

 according to the calculation of Professor Ehreiiberg, no fewer than 

 268 millions might be produced in a month by the repeated sub- 

 divisions of a single Paramecium. When this fission occurs in 

 Vorticella (fig. 593), it extends down the stalk, which thus becomes 

 double for a greater or less part of its length ; and thus a whole 

 bunch of these animalcules may spring (by a repetition of the same 

 process) from one base. In some members of the same family 

 arborescent structures are produced resembling that of Codosiga 



1 Student's Textbook of Zoology, 1898, p. 26. 



- See particularly his memoirs, in vols. vi. and vii. of the second series of the Arcli* 

 Zool. Exper. 1888-i). 



