26 LECTURE II. 



long tentacula ; I will not lay stress on the alimentary canal and 

 appended stomachs, which many still regard as " sub judice ; " but the 

 endowment of distinct organs of generation, for propagating their kind 

 by fertile ova, raises the Polygastric Infusoria much above the mere 

 organic cell. 



In many of the larger species of Polygastria, radiated vesicles, sub- 

 transparent and colourless, generally two in number, and situated 

 near the two extremities of the body, of a highly irritable nature, 

 rapidly contracting and dilating, have been observed. Roesel first 

 figured this contractile vesicle in the Vorticella. In Euodon, in ad- 

 dition to these vesicles, Ehrenberg likewise discerned another organ, 

 of an oval shape, of a dull white colour, and of considerable size, 

 placed in the middle of the abdomen. It is easily detected by the 

 want of colour, when the animal has been well fed and its stomachs 

 filled. This organ is regarded as the testicle, and the contractile 

 radiated bladders as the " vesiculse seminales." The ovarium occupies 

 a more important share of the general cavity of the body : it fills all 

 the interspaces of the stomachs and intestine which are not occupied 

 by the male organs ; and consists of a number of minute corpuscules, 

 or nucleated cells, connected together in a I'eticulate form, generally of 

 a green or pink, or some other bright colour, in well-fed healthy Po- 

 li/gastria. 



The act of generation is attended with the destruction of the parent. 

 The ripe ova burst through some part of the abdominal integument, 

 and escape in a reticulated mass, together with the fertilising fluid. 



By virtue of these diversified modes of multiplication, the powers 

 of ^propagation of these diminutive organised creatures may be truly 

 said to be immense. Malthusian principles, or what are vulgarly 

 so called, have no place in the economy of this department of 

 organised nature. To the first great law imposed on created beings, 

 " increase and multiply," none pay more active obedience than the 

 Infusorial animalcules. 



Attempts have been made to calculate approximatively their rate of 

 increase. 



On the 14th of November, Ehrenberg divided a Paramcecium aurelia, 

 a Polygastric animalcule measuring one twelfth of a line in length, into 

 four parts : which he placed in four separate glasses. 



On the 17th of November, the glasses numbered 1 and 4 each con- 

 tained an isolated Paramsecium, swimming actively about. The 

 pieces in numbers 3 and 4 had disappeared. 



On the 18th there was no change. 



On the 19th each animalcule presented a constriction across the 

 middle of the body. 



