418 



MICROSCOPIC FORMS OF ANIMAL LIFE. 



through the body of the liquid product of the digestive opera- 

 tion, — a surmise which seems in some degree justified by their 

 unusual complexity in Paramecium. For each of its two globu- 

 lar vesicles (Fig. 195, a, a), is surrounded by several elongated 

 cavities, arranged in a radiating manner, so as to give to the 

 whole somewhat of a starlike aspect; and the liquid contents 

 are seen to be propelled from the former into the latter, and 

 vice versd. 



271. Of the Reproduction of the Infusoria, our knowledge is 

 at present very limited ; the attention of observers having, until 

 a comparatively recent period, been fixed almost exclusively 

 upon the act of duplicative subdivision, which, though by far the 

 most frequent method of propagation, is not a true generative 

 operation. It is elfected in the same general mode as the sub- 

 division of Protophyta; and has been observed in many in- 

 stances to commence in the " nucleus" which may usually be 

 distinguished in the cell-bodies of the Infusoi'ia. The division 

 takes place in some species longitudinally, that is, in the di- 

 rection of the greatest length of the body (Fig. 196, d, e, f), in 

 other species transversely (Fig. 199, a, d), whilst in some, as in 

 Ghilodon cuculhdus (Fig. 197), it seems to occur in either direc- 



Fio. 197. 



Fissiparous mulliplicalion of Chilodon cucuUulus: — a, b, c, successive sUiges of longitudinal fission ; 

 D. E, F, successive stages of transverse fission. 



tion indifierently, though there may not improbably be an alter- 

 nation, as there usually is in the direction of the subdivision of 

 the component cells of masses that are increasing both in length 

 and in breadth ( § 195). This operation is performed with such 

 rapidity, under favorable circumstances, that, according to the 

 calculation of Prof. Ehrenberg, no fewer than 268 millions nnght 

 be produced in a month by the repeated subdivisions of a single 

 Paramecium. When this fission occurs in Vorticella (Fig. 196), 

 one of the divisions is usually smaller than the other, sometimes 

 so much so as to look like a bud ; and this usually detaches itself 

 when mature from the main body, and swims freely about until 

 it developes a new footstalk for itself. But sometimes the two 

 parts are equal in size, and the fission extends down the stalk, 

 which thus becomes double for a greater or less part of its length ; 

 and thus a whole bunch of Voi'ticellse may spring (by a repetition 

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

 same family, indeed, an arborescent structure is produced by the 

 like processes of division and gemmation. 



