PJIOTOCOCCUS. 191 



as seen at G, and each of these again undergoing the same 

 division in its turn. Sometimes the contents of the original 

 cell subdivides at once into four, eight, or even thirty-two 

 parts, many of which perish without any further change. 

 The greater number, when set free, possess active powers of 

 movement, and rank as Zoospores, fig. 105 B, which may 

 either develope a loose cellulose investment or cyst, so as 

 to attain the full dimensions of the original motile cell, 

 or may become covered with a dense envelope, losing 

 their vibratile cilia, and thus pass into the dill condition. 

 All these changes, whose relation to each other has been 

 clearly proved by competent observers, have been regarded 

 as constituting, not merely distinct species, but distinct 

 genera of animalcules; such as Cklamydomonas, Euglena, 

 Trackelomonas, Gonium, Pandorina, Uvella, Monas, Astatia, 

 and several others. 



The process of segmentation is often accomplished with 

 great rapidity. Thus it is only necessary to pour the 

 water containing those organisms from a smaller and 

 deeper into a larger and shallower vessel, at once to deter- 

 mine segmentation. The motile cells seem to be favour- 

 ably affected by light, for they collect themselves at the 

 surface of the water and at the edges of the vessel; but 

 when about to undergo segmentation, or pass into the still 

 condition, they sink to the bottom of the vessel, or retreat 

 to that part in which they are least subjected to light: if 

 kept in the dark, they lose most of their colouring matter, 

 and remain stationary, and do not undergo segmentation. 

 Mr. Busk kept his plants for observation in little glass 

 vessels, having the form of a truncated cone, about two 

 inches deep, and one inch and a quarter in diameter, with 

 a flat bottom polished on both sides, aiid filled with water 

 to the depth of from two to three lines. In vessels of this 

 kind he was able to follow the development of a number 

 of various cells throughout. The ordinary small cupping- 

 glass, or glass cells, such as we have described at page 93, 

 answer the purpose equally well. 



Another family of Protophytes, of singular beauty and 

 interest to the microscopist, is the group known as Vol- 

 vodneoBj so closely allied to the former that they have 

 been confounded by more than one observer. 



