INFUSORIA. — OPHRYDIN^. 467 



a vortex in the surrounding fluid, that brought it both food and 

 air. 



350. Another curious departure from the ordinary type is pre- 

 sented by the Family Ophrydince; the Animalcules of which, closely 

 resembling some Vorticellinas in their individual structure, are 

 usually found imbedded in a gelatinous mass of a greenish colour, 

 which is sometimes adherent, sometimes free, and may attain the 

 diameter of four or five inches, presenting such a strong general 

 resemblance to a mass of Nostoc (§ 244) or even of Frogs' spawn, 

 as to have been mistaken for such. The mode in which these 

 masses are produced closely resembles that in which the masses of 

 Mastogloia (§ 234) or of Palmella (§ 239) are formed ; since they 

 simply result from the fact that the multitude of individuals pro- 

 duced 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 com- 

 pletely 'isolated. From a comparison of the dimensions of the 

 individual Ophrydia, each of which is about 1-1 20th of an inch 

 in length, with those of the composite masses, some estimate may 

 be formed of the number included in the latter ; for a cubic inch 

 would contain nearly eight millions of them, if they were closely 

 packed ; and many times that number must exist in the larger 

 masses, even making allowance for the fact that the bodies of the 

 Animalcules are separated from each other by their gelatinous 

 cushion, and that the masses have their central portions occupied 

 only by water. Hence we have, in such clusters, a distinct proof of 

 the extraordinary extent to which multiplication by duplicative sub- 

 division may proceed, without the interposition of any other opera- 

 tion. These Animalcules, however, free themselves at times from 

 their gelatinous bed, and have been observed to undergo an ' encyst- 

 ing-process ' corresponding with that of the Yorticellinje (§ 344). 



351. It is much to be desired that Microscopic observers should 

 devote themselves systematically to the continuous study of even 

 the commonest and best-known forms of Infusory Animalcules; 

 since there is not a single one whose entire Life-history, from one 

 Generative act to another, is known to us. And since it cannot 

 be even guessed at, without such knowledge, what, among the 

 many dissimilar forms that have been described by Prof. Ehrenberg 

 and others, are to be accounted as truly distinct Species, and what 

 are mere phases in the existence of others that are perhaps very 

 dissimilar to them in aspect, it is obvious that no credit is really 

 to be gained by the discovery of any number of apparently-new 

 species, which shall be at all comparable with that to be acquired 

 by the complete and satisfactory elucidation of the Life-history of 

 any one. 



352. As it is among Animalcules that the action of the organs 

 termed Cilia has the most important connection with the vital 

 functions, it seems desirable to introduce here a more particular 



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