MICROSCOPIC FORMS OF ANIMAL LIFE. 4:9 



(K); and the distinction between the newly-formed body to which the 

 cilia belong, and the effete residue of the old, becomes more and more 

 apparent (L). The former increases in size, whilst the latter diminishes; 

 and at last the former makes its escape through an aperture in the wall 

 of the cyst, a part of the latter still remaining within its cavity (M). 

 The body thus discharged (sr) does not differ much in appearance from 

 that of the Oxytricha before its encystment (F), though of only about 

 two-thirds its diameter; but it soon develops itself (o, p, Q) into an 

 Animalcule very different from that in which it originated. First it 

 becomes still smaller, by the discharge of a portion of its substance; 

 numerous very stiff bristle-like organs are developed, on which the Ani- 

 malcule creeps, as by legs, over solid surfaces; the external integument 

 becomes more consolidated on its upper surface, so as to become a kind 

 of carapace; and a mouth is formed by the opening of a slit on one side, 

 in front of which is a single hair-like flagellum, which turns round and 

 round with great rapidity, so as to describe a sort of an inverted cone, 

 whereby a current is brought towards the mouth. This latter form has 

 been described by Prof. Ehrenberg under the name of Aspidisca. It is 

 very much smaller than the larva; the difference being, in fact, twice as 

 great as that which exists between A and P, Q (Fig. 308), since the last 

 two figures are drawn under a magnifying power double that employed 

 for the preceding. How the Aspidisca-foYm in its turn gives origin to 

 the Ozytricha-foYm, has not yet been made out. A similar 'encysting 

 process ' has been observed to take place among several other forms of 

 ciliated Infusoria; so that, considering the strong general resemblance in 

 kind and degree of organization which prevails throughout the group, it 

 does not seem unlikely that it may occur at some stage of the life of 

 nearly all these Animalcules. And it is not improbably in the 'encysted' 

 condition that their dispersion chiefly takes, place, since they have been 

 found to endure desiccation in this state, although in their ordinary con- 

 dition of activity they cannot be dried-up without loss of life. When 

 this circumstance is taken into account, in conjunction with the extraor- 

 dinary rapidity of multiplication of these Animalcules, there seems no 

 difficulty in accounting for the universality of their diffusion. It may 

 be stated as a general fact, that wherever decaying Organic matter exists 

 in a liquid state, and is exposed to air and warmth, it speedily becomes 

 peopled with some or other of these minute inhabitants: and it may be 

 fairly presumed that, as in the case of the Fungi, the dried cysts or 

 germs of Infusoria are everywhere floating about in the air, ready to 

 develop themselves wherever the appropriate conditions are presented; 

 while all our knowledge of their history seems further to justify the 

 belief, that (in some instances, at least) the same germs may develop 

 themselves into a succession of forms so different, as to have been re- 

 garded as distinct specific or even generic types. 



442. A very important advance was supposed to have been made in 

 this direction by the asserted discovery of M. Balbiani 1 that a true 

 process of sexual generation occurs among Infusoria; his observations 

 having led him to the conclusion that male and female organs are com- 

 bined in each individual of the numerous genera he has examined, but 

 that the congress of two individuals is necessary for the impregnation of 



! See his "Recherches sur les Phenomenes Sexuels des Infusoires," in Dr. 

 Brown-Sequard's "Journal de la Physiologic," for 1861. An abstract of these 

 researches is contained in the " Quart. Journ. of Microsc. Science," for July and 

 October, 1862. 

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