780 MICROSCOPIC FORMS OF ANIMAL LIFE 



makes its appearance, and gradually assumes the form of the Tricho- 

 dina grandinella of Ehrenberg. It then develops a posterior wreath 

 of cilia and multiplies by transverse fission ; each half fixes itself by 

 the end on which the mouth is situated, a short stem becomes de- 

 veloped, and the cilia-wreath disappears. A new mouth and cilia- 

 wreath then form at the free extremity, and the growth of the stem 

 completes the development into the true vorticellan form. 1 In 

 Trichoda lynceus, again, the ' encysting process ' appears subservient 

 to a like kind of metamorphosis, the form which emerges from the 

 cyst differing in many respects from that of the animalcule which 

 became encysted. According to M. Jules Haime, by whom this 

 history was very carefully studied,' 2 the form to be considered as the 

 larval one is that shown in fig. 597, A, E, which has been described 

 by Professor Ehrenberg under the name of Oxytricha. This possesses 

 a long, narrow, flattened body, furnished with cilia along the greater 

 part of both margins, and having also at its two extremities a set of 

 larger and stronger hair-like filaments ; and its mouth, which is an 

 oblique slit on the right-hand side of its fore-part, has a fringe of 

 minute cilia on each lip. Through this mouth large particles are not 

 unfrequently swallowed, which are seen lying in the midst of the 

 endosarc without any surrounding vesicle ; and sometimes even an 

 animalcule of the same species, but in a different stage of its life, is 

 seen in the interior of one of these voracious little devourers (B). In 

 this phase of its existence the Trichoda undergoes multiplication by 

 transverse fission, after the ordinary mode (C, D) ; and it is usually 

 one of the short-bodied 'doubles' (E) thus produced that passes 

 into the next phase. This phase consists in the assumption of the 

 globular form and the almost entire loss of the locomotive append- 

 ages (F) ; in the escape of successive portions of the granular proto- 

 plasm, so that ' vacuoles ' make their appearance (G) ; and in the 

 formation of a gelatinous envelope or cyst, which, at first soft, 

 afterwards acquires increased firmness (H). After remaining for 

 some time in this condition, the contents of the cyst become clearly 

 separated from their envelope ; and a space appears on one side, in 

 which ciliary movement can be distinguished (I). This space 

 gradually extends all round, and a further discharge of granular 

 matter takes place from the cyst, by which its form becomes altered 

 (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 (N) does not differ 

 much in appearance from that of the Oxytricha before its encyst- 

 ment (F), though of only about two-thirds its diameter ; but it soon 

 develops itself (0, 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- 



1 Everts, Untersnclmngen an Vorticella nebul/fera, quoted by Professor Allman, 

 toe. cit. 



2 Annales des Set. Nat. ser. iii. tome xix. 1853, p. 109. 



