CCENOBIE.E. 97 



to move with great rapidity. The sixteen cells constituting 

 the first colonies formed in the spring, originate from the 

 repeated division of a single cell, that had passed the winter 



Fig. i8. — Pandorina morum (x 400). A, a motile colony (ccenobium). 

 The individual cells have their cilia protruding through the gelatinous 

 envelope of the colony. B, two zoogonidia, formed by the division of 

 the cells oi A, in process of conjugation. (From Prantl.) 



as a resting-spore. But during the summer, the coenobia, after 

 remaining in a motile state for some time, become quiescent, 

 owing to the retraction of the cilia ; each of the sixteen cells 

 then divides into sixteen smaller cells; the mucilaginous 

 envelope of the ccenobium disappears at this stage and the 

 256 daughter-cells are liberated, each of which secretes a 

 mucilaginous sheath, and forms the starting-point of a new 

 ccenobium. 



Sexual reproduction by conjugation of zoogametes takes 

 place as follows. The sixteen cells of a ccenobium each 

 divide into sixteen daughter-cells, which escape from the 

 colony as motile pear-shaped zoogametes, having bright 



H 



