284 HETEROGENETIC ORIGIN 



and 74, C. This is rendered all the more certain by the fact that 

 the Ciliates which develop from the little spheres shown in the 

 latter figure are embryos, and that no moving thing is ever seen 

 within the egg-cases till these little embryos become roused into 

 active life. 



The notion of ' infection ' is here again an impossible one : it is 

 absolutely incompatible with the facts. It cannot be supposed 

 that 12 to 20 of either of these excessively delicate Ciliates in an 

 embryo condition could penetrate the egg-case^ could devour its 

 contents without being seen, and would then, as embryos, encyst 

 themselves (all in two days, or less) — only, almost immediately after, 

 again to pass out of their encysted condition, and to appear as 

 the active young Vorticellae, or OxytrichcC, whose development 

 I have traced.' 



When the facts recorded in this section are made known to 

 other workers in different parts of the world, some of whom may 

 have no difficulty in finding plenty of material with which to work, 

 and who may be skilled, as I am not, in modern methods of 

 making sections of such minute objects as Hydatina eggs, much 

 highly interesting information, doubtless, will be forthcoming of a 

 nature to satisfy cytologists as to the histological details of the 

 transformation in question. These minute details, however, I 

 must leave to others ; all I claim is to have established the fact 

 itself of the heterogenetic origin of different kinds of Ciliated 

 Infusoria from the eggs of one and the same Rotifer. The 

 seeming utter improbability of such a fact may be taken as some 

 measure of its enormous importance for biological science, when 



• It is, of course, well known that when a Ciliate which has been feeding and 

 leading a free life encysts itself, it usually remains in this condition for weeks 

 or even months, and forms round itself a comparatively thick cyst (as in 

 Fig' 73)i which persists after the Ciliate emerges therefrom, as seen in Fig. 40, B. 

 But a totally different set of things obtains in regard to the embryo Otostomata, 

 the Vorticellae, and the Oxytrichas, with which we are now concerned. They 

 are each of them first seen in the Hydatina egg-cases, motionless, within 

 hyaline cysts which they speedily leave ; the cysts being so delicate that when 

 ruptured they seem not to leave a trace behind. This is the case even with the 

 large Otostomata. Thus, such a hyaline cyst, though so delicate as to be 

 invisible in the photograph, was holding the segments together which are 

 shown in Fig. 69, C ; and a similar very delicate hyaline endocyst formerly 

 enveloped the Otostoma represented in Fig. 65 as escaping from the egg-case — 

 though no trace of it is now to be seen. Yet this delicate endocyst is plainly 

 visible around the stained and contracted embryo shown in Fig. 63. 



