276 HETEROGENETIC ORIGIN 



under the cover-glass, the Rotifer became partly covered by some 

 of the saline concretions, and after various ineffectual attempts 

 to dislodge it I was obliged to be content with photographing it as 

 it is seen in Fig. 71, C (x 150). No other free Otostoma was 

 found beneath this cover-glass. There were only the three within 

 egg-cases, and the one free specimen within the body of the dead 

 Hydatina. This was a very encouraging result, and I have several 

 times tried to get a repetition of it, but as yet ineffectually. 



In the months that these observations were being made, and 

 previously, during prolonged work with other materials taken from 

 the same sites, no Otostomata had ever been seen in association 

 with Hydatina, except those that had been taken from the experi- 

 mental vessels. On two occasions since, however, though from 

 wholly different localities, Otostomata have been found pretty 

 abundantly in association with Hydatins.' The adult forms have 

 been found to be much larger, having from two to three times the 

 length of the great embryos which issue from the egg-cases ; and 

 also to be more highly organised, seeing that what appeared to be 

 a simple contractile vesicle has only once been seen in one of these 

 embryo forms, while it is always present in a developed form, in 

 association with 10 to 12 spindle-shaped radiating channels in the 

 adults. A small specimen of one of these Otostomata, leading a 

 free life, but in a starved state, is shown in Fig. 72 ( x 250), in which 

 the great nucleus and the small ear-shaped mouth are to be seen. 



Many of these adult specimens I have been able to keep for two 

 months, and have seen them pass into an encysted condition. 

 When in this state their bulk is several times greater than that of 

 Hydatina eggs. They are, likewise, enclosed in thick cyst walls, 

 wholly unlike the thin egg-cases of the Hydatina. A rather small 

 specimen in this condition is shown in Fig. 73 ( X 250).^ 



' See " Studies in Heterogenesis," p. 136. It is, of course, quite possible that 

 on certain occasions freshly-laid Hydatina eggs in ditches may be submitted 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, and which then, by some chance, have been partially 

 buried or obscured. Its rarity is indicated by the fact that an Otostoma is only 

 recorded by Saville Kent as having been found once in this country, while this 

 Ciliate is not once referred to by Hickson in his section on the Ciliata in Ray 

 Lankester's "Treatise on Zoology." 



' The subsequent fate of some of these encysted specimens is described in 

 " Studies in Heterogenesis," p. 285. 



