272 HETEROGENETIO ORIGIN 



almost invariably when these Rotifers have been kept long in 

 confinement. All stages may, indeed, often be seen between 

 the ordinary eggs full of blackish granules that are to be found in 

 these media (both free and within the bodies of the Hydatinas), 

 and the similar black granule eggs to which a thick hirsute 

 envelope is added — that may also be seen both free and within 

 the bodies of the parent Hydatinse. 



When masses of eggs of this kind, which for brevity we may 

 speak of as ' black granule eggs,' are taken and batches of them 

 are placed in pots in the usual way, those that are freshly laid 

 undergo the transformation into Otostomata, in the manner I have 

 described ; and the Ciliates to which they give rise are also filled 

 with black granules during their formation and when they emerge 

 from the egg-cases. Thus Fig. 70, A (x 125) shows one of these 

 black granule eggs ; while B (x 125) shows another that had gone 

 on to the formation of a Ciliate densely packed with black granules. 

 This was now segmented into two, and, before the application of 

 a formalin solution, each segment was very slowly moving within 

 the egg-case. Although no large corpuscles are to be seen in the 

 photograph, yet examination of the specimen with the microscope 

 showed that they were present though hidden by the abundance 

 of granules. Of course no such complete segmentation as this, 

 with slow rotations of the separate parts, is ever to be seen during 

 the ordinary development of a Hydatina egg. 



In D (x 250) we have represented a specimen of one of the great 

 Otostomas, just after it had emerged from the case of one of these 

 black granule eggs. The granules in it do not completely hide the 

 globules, and the appearance of these within this ciliated organism 

 is strikingly like the vesicles which enter so largely into the com- 

 position of the egg-mass during earlier periods of the transformative 

 process. C ( x 250) shows one of the products of fission of a Ciliate 

 formed from such an egg. In it the granules are again so abundant 

 as almost completely to hide the usual great globules which it also 

 contains. In E ( X 80) there is shown, at a much lower magnifica- 

 tion, a group of Otostomas produced from black granule eggs, 

 situated among a mass of egg-cases from which Hydatinje had 

 escaped. Most of the Ciliates were seen revolving within their 

 egg-cases, though others had escaped and, before they were killed 

 with a weak formalin solution, were slowly moving among the 

 empty cases. These empty egg-cases had been left by Rotifers 

 which had already commenced their development before having 



