POLYGASTKIA. 35 



spontaneous division : in No. 4. eight individuals had in like manner 

 been generated. 



On the 21st no change had taken place. 



On tlie 22nd there were six nearly equal-sized individuals in No. 1., 

 and eighteen individuals in No. 4. 



On the 23rd, the individuals wei'e too numerous to be counted. 



Thus it was demonstrated that this species of Polygastrian would 

 continue for six days without any diminution of reproductive force, 

 and that on one day a single individual twice divided, and one of its 

 divisions effected a third fission. 



A similar experiment on a Stijionychia Mytilus, an animalcule one 

 tenth of a line in length, was attended with nearly the same results ; 

 it was well supplied with the green nutrient matter, consisting of the 

 Monas pulvisculus, and on the fifth day the individuals generated by 

 successive divisions were too numerous to be counted. 



The conditions of this parthenogenetic mode of propagation appear 

 to be the close conformity of the entire Polygasti-ian to the condi- 

 tion of the nucleated cell, the attractive and assimilative force of the 

 nucleus, and the large proportion of unchanged secondary cells in its 

 organisation. 



Cells predominate in the tissues of the vegetable kingdom, the 

 lower members of which consist exclusively of them, and have been 

 thence called ' plantiB cellulares :' the lowest of all consist of a single 

 nucleated cell. 



The animal kingdom starts from the same elementary beginning : 

 a cell-wall forms the smooth elastic and contractile integument of 

 the Gregarina — a genus of microscopic parasites which infest gre- 

 gariously the internal cavities and canals of insects and worms — in 

 which a fluid with granules, and a firm nucleus with sometimes a 

 nucleolus, are the sole representatives of organs or viscera. Yet 

 the power of the Gregarince to live and grow independently by assi- 

 milating foreign nutriment, the vital contractility of their tegu- 

 mentary tunic, their chemical composition and their definite forms, 

 with such well-marked specific characters, in a few instances, as 

 the Greg, brevirostris and Greg. Sieholdii present, render their in- 

 terpretation by Kolliker as a low and primitive form of parasitic 

 animal, the most accordant with actual physiological and zoological 

 knowledge.* 



The Gregarina is a single-celled animal, which diff*ers from the 

 single-celled plant by the vital contractility of its tissue, and the solu- 

 bility of its cell-wall in acetic acid. Devoid of mouth, stomach, or 



* VII. p. 10. 



D 2 



