34 LECTURE II. 



The Vorticella microstoma secretes, and surrounds itself by, a 

 smooth cyst, in which all its previous organisation is resolved into 

 a minutely granular fluid, save the pulsatile sac, which ceases to beat, 

 and the elongated bent nucleus. Two processes of development start 

 from this partial dissolution and passive pupal condition. In the one 

 (acinetiform) process the nucleus contracts itself into a shorter and 

 thicker shape ; two pulsatile sacs are developed ; and a new integu- 

 ment is formed, from which radiate groups of long vibratile filaments. 

 The creature thus starts afresh into locomotive life as an Actino- 

 phrys ; and then developes a hollow stem, and becomes the Acineta 

 mystacina of Ehrenberg.* In this the nucleus expands, attracts 

 and assimilates the surrounding granular fluid, and becomes deve- 

 loped into a pyriform monad with a circular band of vibratile cilia : the 

 embryo escapes from the Acineta, swims otf, and lays the foundation 

 of a new colony of Vorticellce. In the second (monadiform) process 

 of development the nucleus of the encysted pupa elongates and 

 divides by spontaneous flssion into many nucleoli : each of these 

 exercises its attractive, assimilative, and modifying properties upon 

 the contiguous granular fluid : as many minute simple locomotive 

 monads are the result, wliich escape from a rent in the cyst, and 

 swim abroad, doubtless to undergo further changes, completing the 

 metagenetic cycle, f 



By virtue of these diversified modes of multiijlication, the powers 

 of propagation of the most diminutive of 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 orga- 

 nised 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 Paraw«;ctMm 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 Paramaacium, swimming actively about. The 

 pieces in numbers 2 and 3 had disappeared. 



On the 18th there was no change. 



On the 19th each animalcule presented a constriction across the 

 middle of the body. 



On the 20th No. 1. had propagated five individuals by transverse 



* XI., tab. XX., fig. X. t XXV*, pp. 478—485, XVIIL, fig. 1 — 13. 



