OF THE EOTATOEIA. 465' 



Indeed the Kotatoria, in part at least, have a remarkable power of preserv- 

 ing theii' vitality, not only when left dry by ordinary evaporation, but also 

 when thoroughly desiccated by the assistance of heat. Leuwenhoek and 

 Spallanzani experimented on them, and announced the fact of their revivifi- 

 cation on the addition of moistm^e, months and even years after their com- 

 plete desiccation. Schrank, Bory St. Vincent, and Ehi-enberg questioned the 

 tnith of this statement, at least in its full acceptation ; and the Avriter last- 

 named affirmed " that wherever these creatures are completely desiccated, 

 life can never again be restored. In this respect the Rotifera exactly 

 coiTcspond with animals of a larger kind : like them, for a time they may 

 continue in a lethargic and motionless condition; but, as is well known, 

 there will be going on within them a consumption or wasting away of the 

 body, equivalent to so much nourishment from without as would be needed 

 for the sustentation of life." ^N'either the last statement nor those preceding 

 it are correct ; MM. Schultze and Doyere have repeated and confiiined the 

 experiments of the old observers ; and the latter authority concludes that 

 Eotifera may be completely diicd in pure sand in the open aii% and in a 

 vacuum, without losing the capability of being re\'ived by moistiu-e. Many 

 indeed are sacrificed in the process ; but enough recover to demonstrate the 

 possibihty of the fact. 



This extraordinaiy power of resiLScitation after di^ying explains the re- 

 appearance of Eotatoria on the collection of water in shallow pools which 

 have been entirely dried up by the hot sun of summer, and their con- 

 stant presence in the diy debris of the roofs, and even of the interiors of 

 houses. 



In their relation to temperature, also, the Rotatoria exhibit great tolerance. 

 M. Doyere proved that when placed in water at fi^om 113° to 118°, they 

 could afterwards be re\ived, but that when thrown suddenly into boiling 

 water (at 212°) they were at once killed. In the latter case, the sudden 

 heating is supposed to coagulate the albuminoid contents of the animals, and 

 in that way to cause death, because individuals previously dried by a gradually 

 raised heat of 216°, 252°, and even of 261°, were many of them still capable 

 of being revived. 



On the other hand, Rotatoria can live in water at the freezing-point. They 

 are to be found under ice, and also within the hollow ca^'ities of ice ; and 

 Perty mentions a score of species which he met with in such localities. He 

 also recounts meeting with individuals contracted in a more or less globular 

 figm-e, preparatory, as he sunnises, to a winter sleep or torpor. He figiu'es 

 a PhUodina erytlirophthahna (XXXYIII. 4) in this condition, which is pre- 

 cisely the same as that assumed when the animal is left dry ; and he adds 

 that when Scaridium longicaudum assumes this state, it withdraws its head 

 within its envelope and doubles its tail under the abdomen, just in the same 

 way as a Podura. Ehrenberg doubtless refers to this same contracted con- 

 dition in the account before quoted from him (p. 449-50) respecting the 

 Rotifera found at great altitudes among snow, which he described as having 

 an ovate figui'e and enclosed in an egg-shaped envelope. 



Conochilus and Lacimdaria are examples of Rotifera living in aggregated 

 masses. The former recalls, by its compoimd revohing spheres, the appear- 

 ance of Vohox Glohator, whilst the latter occurs in small transparent jelly- 

 like balls adherent to the leaves of aquatic plants. 



At times the Rotatoria multiply so rapidly in smaU stagnant pools as to 

 eoloiu^ the water. Hi/datina senta, Diylena catellina, Triartlira, and Lepa- 

 della are adduced by Ehrenberg as producing a milky turbidity in water, and 

 the Typldlna viridis as imparting a green colour. 



2h 



