146 GENERAL HISTORY OF THE INFUSORIA. 



alike in the three genera in question, the bisection of the contents of the 

 cell proceeding so far that they are eventually resolved into numberless small, 

 mostly spindle-shaped corpuscles (XIX. 51), which at first oscillate by the 

 aid of two or four \ibratile filaments mthin the common envelope-cell, but 

 subsequently escape singly from it, (XIX. 52), and, after enjoying for a con- 

 siderable time very energetic infusorial movements, finally pass into a state 

 of rest, preparatory to some futui'e development. 



" The larger undivided macrogonidia, after swarming often the whole day, 

 are also seen to enter (as ^vitnessed in Chlami/dococcus and Steplianosphcera) 

 into the condition of rest, when each primordial cell contained within the 

 delicate envelope-cell secretes about itself a second more compact cellulose 

 membrane which closely invests it, and is not perforated by the ciliary fila- 

 ments (XIX. 20, 21). It is, in fact, the countei^part of the membrane which, 

 in common plant-cells, overhes the primordial layer. In tliis distinctly 

 plant-like or protococcoid condition the cells remain without motion, and 

 may endure, even when dried, for a whole year, and then, on the addition of 

 water, undergo segmentation into two, foui', or eight gonidia, which, imme- 

 diately after developing their filaments and envelope-cells, break through the 

 walls of the parent -cell and crowd the surrounding fluid." 



The facts relating to the structure and functions of the genera above 

 adduced, apply in the main to all the Volvocinece ; for the diff'erences between 

 the several genera, although demanding special consideration, are not essen- 

 tial. Thus, for example, in Gonium (XIX. 32) the figiu'e is a flattened sphe- 

 roid, and the green primordial cells, \iewed collectively fi'om above, resemble 

 a four- sided disc or plate, having each angle truncated. Moreover, the trans- 

 parent coloiu'less envelope does not acquire the character and appearance of 

 a firm membrane, but presents itself as a mucous or gelatinous, not cellulose, 

 sheath. 



Chlamydomonas. — The first of the genera included by Ehrenberg in his 

 family Vohocina, of which we shaU attempt a description, is Chlamidomonas 

 or Chlamydomonas (XIX. 16). It recommends itseK to our attention because 

 of its simplicity and its existence in an isolated state. This last fact seemed 

 to Dujardin a sufiicient reason for remo^dng it from the Volvocina to the 

 Thecamonadina, and for renaming it Disehnis, on accoimt of its having two 

 filaments ; for he would admit into the former family only aggregate organ- 

 isms " enclosed within a common envelope, or ha\'ing special envelopes 

 mutually adherent." On this same ground he also advocated the transposi- 

 tion of Gyges from the Volvo.v family to that of the Thecamonadina, a genus 

 which we shall presently have to note under the name of Chlamydococcus or 

 Profococcus pluviaVis. To this arrangement Cohn objects {A. N. H. 1852, 

 X. p. 334) ; for, says he, '' a more profound investigation, not only of the 

 structure, but also of the history of development, teaches us that Chlamydo- 

 monas (Disehnis, Duj.) possesses only external analogies with Trachelomonas, 

 while this form, as Ehrenberg abeady discovered, exhibits the closest alhance 

 to Gonium and Pandorina. The relation of the colourless envelope to the 

 enclosed green globes, the position of the two ciha, which arise from the latter 

 and pass out through the former, and lastly, the laws of division of the green 

 cells inside the envelope, in powers of two, display themselves in exactly the 

 same way in Chlamydococcus as in the rest of the Volvocinece ; and the only 

 distinction between them consists in the circumstance that in Chlamydomonas 

 (and Chlamydococcus) the individuals produced by the di\-ision of the green 

 globes separate after the absorption of the parent envelope, and live on as 

 individuals, while in the other Volvocineoi the daughter- cells produced by 

 the division of one green primordial cell remain connected by the persistent 



