MICROSCOPIC FORMS OF ANIMAL LIFE. 59 



some other instances the eggs, after their extrusion, remain attached to 

 the posterior extremity of the body (Fig. 309), until the young are set 

 free. The transparence of the egg-membrane, and also of the tissues, of 

 the parent Rotifer, allows the process of development to be watched, 

 even when the egg is retained within the body; and it is curious to ob- 

 serve, at a very early period, not merely the red eye spot of the embryo, 

 but also a distinct ciliary movement. " In general it would seem that 

 whether the rupture of the egg-membrane takes- place before or after the 

 egg has left the body, the germinal mass within it is developed at once 

 into the form of the young animal, which usually resembles that of its 

 parent; 110 preliminary metamorphosis being gone through, nor any 

 parts developed which are not to be permanent. In Floscularia ornata, 

 however, the young leave the eggs in the shape of little maggots, from 

 one end of which a tuft of cilia soon appears. The form changes in a 

 few hours, the ciliated end becoming lobed, and the body rounded. The 

 foot is developed later. 1 In the curious Notommata Werneckii, which is 

 found parasitic in the reproductive capsules of Vauclieria ( 249), the 

 young animal has the general organization of the free-swimming Eotifers, 

 and leads a similarly active life; but when its eggs are becoming mature, 

 it finds its way into one of these capsules and there undergoes a remark- 

 able deformation, its characteristic organs disappearing, and its body be- 

 coming a large egg-sac, which seems to be nourished by absorption. 9 



451. Even in those species which usually hatch their eggs within 

 their bodies, a different set of Ova is occasionally developed, which are 

 furnished with a thick glutinous investment; these, which are extruded 

 entire, and are laid one upon another, so as at last to form masses of 

 considerable size in proportion to the bulk of the animals, seem not to be 

 destined to come so early to maturity, but very probably remain dormant 

 during the whole winter season, so as to produce a new brood in the 

 spring. These ' winter-eggs ' are inferred by Prof. Huxley, from the 

 history of their development, to be really gemmce produced by a non- 

 sexual operation; while the bodies ordinarily known as ova, he considers 

 to be true generative products. Prof. Cchn, however, states that he has 

 ascertained, by direct experiment upon those species in which the sexes 

 are distinct, that the bodies commonly termed ' ova' (Figs. 309, 310) are 

 really internal gemmce, since they are reproduced, through many succes- 

 sions, without any sexual process, just like the external gemmae of Hydra 

 ( 515), or the internal gemmae of Entomostraca ( 609) and Aphides 

 ( 643); whilst the ' winter-eggs,' are only produced as the result of a 

 true generative act. 3 By M. Balbiani, however, it is affirmed (loc. cit.} 

 that the 'winter-eggs,' like the ordinary eggs, are produced non-sexually; 

 so that it would seem as if the intervention of the true generative act is 

 only occasionally required for the continued propagation of these inter- 

 esting creatures. 



452. Certain Rotifera, among them the common Wheel-Animalcule,, 

 are remarkable for their tenacity of life, even when reduced to such a 

 state of dryness that they will break in pieces when touched with the 

 point of a needle (as the Author Jias himself ascertained); for they can 

 be kept in this condition for any length of time, and will yet revive very 

 speedily upon being moistened. Taking advantage of this fact, some- 



1 See Mr. Slack's " Marvels of Pond Life," 3d Edit., p. 54. 



2 See Balbiani in " Journ. Roy. Microsc. Soc.," Vol. ii. (1879), p. 530. 



3 See his Memoir, ' Ueber die Fortpflanzung der Raderthiere,' in " Sie-ho 

 Kolliker's Zeitschrift," 1855. 



