INFUSORIAL ANIMALCULES. 7l 



single specimen of Hydatina senta^ and kept it in a sepa- 

 rate vessel for eighteen days, that during this interval it 

 laid four eggs per day, and that these young, at two days 

 old, lay a like number, so that, when circumstances are 

 favourable, one million individuals are obtained from one 

 specimen in 10 days; that, on the eleventh day, this 

 brood will amount to four millions, and on the 1 2th day 

 to sixteen milhons. Although the fecundity of this 

 Rotatoria is the greatest that has been tested by direct 

 experiment, yet in the large Polygastrica, as the Para- 

 mecium aurelia, a single specimen in one day is ascertained 

 to increase to eight, by simple transverse division of the 

 body only ; so that, if we take into this account the other 

 modes of the increase of this creature, namely, by eggs, 

 often in masses like the spawn of fish, and again by buds 

 growing from the sides of the body, it is clear, in a very 

 few days, all attempt at an expression of their number 

 must fail. 



Section XXXII. — Vascular System. 



In several of the Rotatorial Infusoria are observed 

 transverse vessels, which have the appearance of articula- 

 lations. In others, these vessels resemble a net work (see 

 pi. vs., fig. 419), which is more or less distinct, below the 

 edges of the mouth, and connected by free longitudinal 

 ones to the interior ventral surface of the body. 



Oval tremulous little bodies are in some species observed 

 attached to a free filament-like tube (Notommata, fig. 

 416), generally disposed longitudinally within the body 

 of the animalcules. Sometimes these little bodies are 



