2i6 Hardy, A Red Euglena. [^Mardf' 



of temperature, or when the surface of the water is much dis- 

 turbed by wind, to reappear during the next calm, hot period. 



There is, however, one hole that differs from others of the 

 locality in having less surface and greater depth (these being 

 about 3 metres and average 2.5 metres respectively), while, 

 instead of the water being coloured and impinging on sloping 

 clayey banks at the surface, as in the case of the dams, &c., 

 it is colourless, and in contact with the humic layer which 

 underlies the grasses which surround it. This hole has its supply 

 considerably increased by a natural gutter draining from the 

 country road. From the owner of the orchard I learned that 

 this hole was in part formed by the grubbing of an old eucalypt 

 stump, which left an excavation 1.5 m deep, which filled with 

 water, and remained so for some years without any scum, 

 green or red, appearing. In 1904 the hole was deepened by 

 the removal of stone from the bottom, and the present depth 

 attained. In the following and succeeding few years the red 

 scum appeared regularly during air temperatures of between 

 90° and 100° Fahr., until the summer of 1907-8, during which 

 there was not a sufficient duration of heat to produce a visible 

 scum on any of the pools, nor has the red form appeared since 

 in that locality, although a sraall quantity of E. viridis was 

 evident on two occasions on the surface of neighbouring dams. 



Although in the red scum E. rubra predominated, there 

 was present, though not macroscopically, a small quantity 

 (about I per cent.) of E. viridis. Necessarily, the search 

 amongst countless myriads of organisms of a kind for some- 

 thing abnormal must be inexhaustive, but in the many samples 

 taken from other waters in which E. viridis was plentiful, not 

 a single red organism was seen, nor was there any trace of red 

 colour, excepting the "eye-speck," observed in any of the many 

 thousands of E. viridis from those localities or from the pool 

 containing the red form. 



Between the largest specimen of E. viridis and the smallest 

 of the red form there was a noticeable interval which I failed to 

 bridge (for difference in average size see Plate xviii. — fig. i, 

 E. rubra ; fig. 2, E. viridis) ; but, according to measurements 

 given by Saville Kent, this difference holds good only for this 

 region.* After due consideration of Saville Kent's statement, 

 when rejecting Ehrenberg's E. sanguinea, to the effect that 

 the red colour was merely one of the mature phases of E. 

 vifidis which he had proved by experiment was capable of 

 ingesting particles of carmine in solution, I cannot make it 

 apply to the species under consideration. E. viridis is generally 



* The " Cambridge Natural History " gives I mm for length of £. viridis, 

 which, while falling short of that given by Saville Kent, Parker, and other 

 observers, agrees better with what I have personally seen. 



