MICROSCOPIC FORMS OF ANIMAL LIFE 



(fig. 586) by the like process of continuous subdivision. Another 

 curious result of this mode of multiplication presents itself in. 

 the family Ophrydina, masses of individuals which separately resemble 

 certain Vorticellina being found imbedded in a gelatinous substance of 

 a greenish colour, sometimes adherent and sometimes free. These 

 masses, which may attain the diameter of four or five inches, present 

 such a strong general resemblance to a mass of Xostoc, or even of frog's 

 spawn, as to have been mistaken for such ; but they simply result from 

 the fact that the multitude of individuals produced by a repetition of 

 the process of self-division remain connected with each other for a 

 time by a gelatinous exudation from the surface of their bodies, 

 instead of at once becoming completely isolated. From a comparison of 

 the dimensions of the individual Ophryda, each of which is about i4^th 

 of an inch in length, with those of the composite masses, some estimate 



3 may be formed of the 



number included in 

 the latter; for a 

 cubic inch would con- 

 tain nearly eight 'mil- 

 lions of them if closely 

 packed ; arid many 

 times that number 

 must exist in the 

 larger masses, even 

 making allowance for 

 the fact that the 

 bodies of the animal- 

 cules are separated 

 from each other 

 by their gelatinous 

 cushion, and that 

 the masses have their central portions occupied by water only. 

 Hence we have, in such clusters, a distinct proof of the extra- 

 ordinary extent to which multiplication by duplicative subdivision 

 may proceed without the interposition .of aiiv other operation. 

 These animalcules, however, free themselves at times from their 

 gelatinous bed, and have been observed to undergo an 'encysting 

 process ' corresponding with that of the Vorticellina. The chemical 

 composition of this jelly or zoocytium has been investigated by 

 Halliburton, who finds that it resembles vegetable cellulose in its 

 general properties, but differs from it and agrees w r ith the form of 

 cellulose manufactured by the Tunicata in being less easily converted 

 into sugar. 



Many, perhaps all, ciliated Infusoria at certain times undergo an 

 encysting process, resembling the passage of protophytes into the ' still ' 

 condition, and apparently serving like it as a provision for their pre- 

 servation under circumstances which do not permit the continuance 

 of their ordinary vital activity. Previously to the formation of the 

 cyst, the movements of the animalcule dimmish in vigour, and 

 gradually cease altogether ; its form becomes more rounded ; its 

 oral aperture closes ; and its cilia or other filamentous prolonga- 



FIG. 594. Reproduction of Infusoria. 



