1912.] A Note on the Protozoa from Sick Soils. 



397 



chromatin granules (fig. 4). A curious feature in this division is the 

 apparent increase in the amount of chromatin in the nucleus during the 

 early stages of division, an increase which it seems difficult to account for 

 when one considers the amount of chromatin in the caryosome and on the 

 wall of the resting nucleus (fig. 5). One of the division-products of the 

 blepharoplast, with its fiagellum, now passes around the nucleus, being still 

 connected with the other blepharoplast by a faintly staining strand, which 

 seems to have more affinity for eosin than for chromatin stains (vide figs. 5 

 and 6). 



The chromatin granules are now massed in an irregular oval body on the 

 strand connecting the two blepharoplasts, as is shown in figs. 5 and 6. The 

 chromatin masses then appear to stream in an irregular manner towards 

 either blepharoplast. There they become collected into two crescent-shaped 

 masses, in the convexity of each of which a blepharoplast lies (fig. 7). At 

 the same time the body of the flagellate becomes much elongated in the axis 

 of the line joining the two blepharoplasts. About this stage there seems to 

 be mysterious diminution in the amount of chromatin comparable to the 

 increase which was noted in the early stages of division. The body of the 

 flagellate now becomes constricted (fig. 8) and the division-products separate 

 (fig. 9). It seems probable, from the relative frequency with which the 

 stages are met on the stained films, that the early stages of division are 

 much slower than the later. 



Before proceeding to a description of the process of encystation in this 

 flagellate, I should like to draw attention to some features in the behaviour of 

 the cultures with regard to the life-cycle of this animal. In the first place, 

 the appearance of an encystation-epidemic in any particular culture seems to 

 be primarily due to the amount of moisture on the culture-plate. I have, on 

 several occasions, started series of three parallel cultures : (a) rather dry, 

 (b) fairly moist, and (c) quite moist. In all three the organisms would do 

 well at a temperature of about 18° C, with the result that at the end of 

 the third day the fixed films of any culture would show a large number of 

 division-figures. An encystation-epidemic would, however, set in in (a) at 

 the end of a week, in (b) at the end of about 12 days, whereas cultures of the 

 type of (c) have been kept over two months without the appearance of 

 encystation. 



What the ultimate factor in this appearance of encystation-epidemics in 

 drying cultures may be I should not at present care to hazard an opinion. 

 Possibly it may be simply a direct osmotic effect upon the animal, possibly it 

 may introduce changes in the bacterial flora of the plate resulting in a 

 diminution of the appropriate food-supply of the animal, or possibly it may 



2 E 2 



