
1905.]  Ciliated Infusoria within the Eggs of a Rotifer. 389 
capable of passing through wood but not through stone, notably hastens the 
process. 
Briefly enumerated, the stages of the transformation are these :— 
(1) A freshly laid Hydatina egg; (2) partial rearrangement of its contents 
on the way to the formation of a mass of small vesicles; (3) the conversion 
of the major part of the egg substance into a mass of spherical vesicles of 
varying sizes; (4) further changes in the aggregate of vesicles and intervening 
granules ; (5) the formation of the embryo Otostoma within an almost 
invisible hyaline endocyst; (6) the development of cilia and the slow 
rotation of the embryo within this envelope; (7) the bursting of the hyaline 
envelope, with freer play of cilia and more rapid movements within the egg- 
case ; (8) in some instances fission into two, four, or more, active segments ; 
(9) rupture of the Rotifer egg-case, and the appearance of its contents in the 
form of a very large and rapidly moving Ciliated Infusorium belonging to 
the genus Otostoma. 
During a period of eight or nine months in which I was working at this 
subject, off and on, I took some hundreds of the Otostomata in different stages 
of development from the experimental vessels. On one occasion I found two 
eggs within a dead Hydatina in a vesicular condition like that shown in 
figs. 3 and 4; and on another occasion I found a living Otostoma within a dead 
Hydatina, as an outcome probably from such an egg. Details as to the conditions 
under which they were met with are given in my “ Studies in Heterogenesis,” 
pp. 133 to 136; and in the same work full particulars will be found of the 
transformation of the eggs of another Rotifer (belonging to the genus 
Callidina) within the dead bodies of the parents into a different kind of 
Ciliate, belonging to the genus Glaucoma—showing that the origin of 
Otostoma in the manner indicated in this paper is far from being an isolated 
occurrence. 
In the months that these observations were being made, and previously, 
during prolonged work with other materials taken from the same site, 
no Otostomata had ever been seen in association with Hydatine, except those 
that had been taken from the experimental vessels. On two occasions since, 
however, though from wholly different localities, Otostomata have been found 
pretty abundantly in association with Hydatine.* The adult forms have been 
* It is, of course, quite possible that on certain occasions freshly-laid Hydatina eggs in 
ditches may be exposed to much the same kind of conditions as those to which they 
would be exposed in my experimental vessels. That such a transformation does not 
occur oftener depends probably upon the fact that it can only be brought about in eggs 
which have been quite freshly laid. 
