CHAIN FORMATION BY FRONTONIA. 



259 



isolation, it becomes transformed by clearing of the pigment, 

 lengthening and flattening the general shape of the body until 

 it resembles the well-known species Frontonia leucas. To this 

 species, therefore, I have assigned my material, although I am 

 not positive whether what I have observed is a new stage in the 

 life-cycle of Frontonia leucas or a new species. 



The process of chain formation is inaugurated by the formation 

 of a large transparent cyst through the exudation of some gelati- 

 nous material in which the surrounding zooglcea becomes en- 

 tangled in large quantities. Within this cyst the individual 

 slowly rotates, all the cilia beating and the contractile vacuole 

 pulsating regularly. In one individual followed under the mic- 

 roscope a single transverse division occured about forty-five 

 minutes after the beginning of encystment, and half an hour 

 from its completion. Nine hours after, the daughter cells were 

 dead, still connected and inside the cyst wall. 



FIG. i. Chain of four cells, Frontonia leucas. 200 X. Outline drawn with 

 camera from preparation fixed with sublimate-acetic and stained with picro- 

 carmine. Details restored from free-hand drawings of living material. 



Another encysted individual which had been isolated at 

 the same time but which unfortunately had not been followed 

 under the microscope had formed a chain of four cells. The 

 writer has at different times observed in these cysts, single, 

 double, and quadruple forms, as well as cysts containing two or 

 four separate cells. One chain of four individuals was removed 

 from its cyst for observation: it swam about for a time resembling 

 an animated chain of beads, but finally broke up into its four 



