266 HBTEROGENETIC OEIGIN 



a good hand lens), and also for any eggs in the intermediate 

 vesicular stages above referred to. I have invariably found that 

 such a search yielded only negative results. 



In taking batches of eggs, in the manner indicated, to be placed 

 in the pots, individual eggs will necessarily be of different ages. 

 Some will have already begun to develop into Rotifers, and some 

 of these, under the altogether unnatural conditions to which they 

 are subjected in the dark pots, are apt to become more or less 

 malformed as development proceeds. Others, that have been 

 quite recently laid, will not have begun to develop, and it is these 

 latter eggs apparently, which, under the cutting off not only of 

 ordinary light but probably of some invisible light rays, become 

 speedily transformed into great Ciliated Infusoria. Cutting off 

 ordinary light rays alone from the eggs, by placing them in a small 

 covered glass dish shut up in a cupboard or box, and maintained at 

 the same temperature as before, seemed at first not to lead to 

 similar results ; but I subsequently ascertained that the transfor- 

 mation will occur under such conditions, though only after the 

 lapse of about nine, rather than three, days. It looks, therefore, as 

 if the stoppage of some invisible rays, capable of passing through 

 wood but not through stone, notably hastens the transformation. 



After this brief summary of the course of events during this 

 remarkable transformation, the details may now be illustrated by a 

 series of photomicrographs. 



The changes in question occur with equal proportionate fre- 

 quency in the large and the small eggs laid by Hydatinse. It 

 needs only a comparatively brief acquaintance with these creatures 

 to recognise that their eggs vary a good deal in size. It is com- 

 monly believed, and I think with truth, that the smallest of the 

 eggs give birth to the small male Hydatinze. But between such 

 small eggs and the large eggs there is no abrupt demarcation. 

 There are plenty of eggs also of intermediate dimensions, and 

 these give birth to female Hydatinae, although to specimens falling 

 short of the full size. 



I shall show some of the stages of these transformative changes, 

 leading to the production of Otostomas, first of all in large eggs, 

 and subsequently in the small specimens. 



In Fig. 6i, all the components of which are magnified 250 

 diameters, the early changes leading to the production of the great 

 Ciliate are represented. One of the large eggs recently laid is 



