AND ITS REVELATIOINS. 235 



those of generation. It would appear, therefore, quite unfit to obtain 

 aliment for itself ; and its existence is probably a very brief one, being con- 

 tinued onl}- so long as the store of nutriment supplied by the egg remains 

 unexhausted. In Rotifer, however, as in by far the larger proportion of 

 the class, no males have been discovered ; and it remains doubtful whether 

 the two sexes are united in the same individual, or whether the males are 

 produced only at certain times. The female organ consists but of a single 

 ovarian sac, which frequently occupies a large part of the cavity of the 

 body, and which opens at its lower end by a narrow orifice into the cloaca. 

 Although the number of eggs in these animals is so small, yet the rapidity 

 with which the whole process of their development and maturation is ac- 

 complished, renders the multiplication of the race very rapid. The egg of 

 the Ilydatina is extruded from the cloaca within a few hours after the 

 first rudiment of it is visible ; and within twelve hours more the shell 

 bursts, and the j'oung animal comes forth. In the Botifer and several 

 other genera, the development of the embryo takes place whilst the egg is 

 yet retained within the body of the parent (fig. 201, h), and the young are 

 extruded alive ; whilst in some other instances, the eggs, after their extru- 

 sion, remain attached to the posterior extremity of the body (fig. 200), until 

 the yoimg are set free. In general it would seem that, whether the rup- 

 ture of the egg-membrane takes place before or after the egg has left the 

 body, the germinal mass v.'ithin it is developed at once into the form of the 

 young animal, which resembles that of its parent ; no preliminary meta- 

 morphosis being gone through, nor any parts developed which are not to be 

 permanent. The transparency 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 observe, at a very early period, not merely the red eye-spot of the em- 

 bryo, but also a distinct ciliary movement. The multiplication of Hydatina 

 (in which genus three or four eggs are deposited at once, and their deve- 

 lopment completed out of the body) takes place so rapidly, that, according 

 to the estimate of Professor Ehrenberg, nearly seventeen millions may be 

 produced within twenty-four days from a single individual. 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 matu- 

 rity, but very probably remain dormant during the whole winter season, 

 so as to produce a new brood in the spring. These ' winter-eggs' are in- 

 ferred by Mr. Huxley, from the history of their development, to be really 

 (jemmK produced by a non-sexual operation ; while the bodies commonly 

 called ova, he considers to be true generative products. Dr. Cohn has 

 recently informed the author, however, that he has ascertained by direct 

 experiment upon those species in which the sexes are distinct, that the 

 bodies commonly termed ova (figs. 200, 201), are really internal gemmce, 

 since they are reproduced, through many successions, without any sexual 

 process, just like the external gemmaj of Hydra (§ 301), or the internal 

 gemma; of Entomostraca and Aphides (Chap. xvi). And this view appears 

 to himself to be more accordant \vith general physiological analog)^, than 

 that of Mr. Huxley, since, in the other instances referred to, as in the 

 Rotifera, the multiplication by gemmation goes on rapidly whilst food and 

 warmth are abundantly supplied ; but gives place to the true generative 

 process, when the nutritive activity is lowered by their withdrawal." 



Although, of course, Dr. Carpenter has drawn largely on 

 the researches of others, the work contains much matter which 



