500 PROFESSOR E. RAY LANKESTER. 
exhibit, according to undetermined conditions, all or some of 
these forms, was definitely and precisely formulated by me in 
my memoir on “ A Peach-coloured Bacterium,” published in 
the ‘ Quart. Journ. of Micro. Science’ in 1873. I distinctly 
recognised the existence of true species of Bacteria or Schizo- 
phyta, but I pointed out that these must be characterised, not 
by the simple form-features used by Cohn, but by the 
ensemble of their morphological and physiological properties 
as exhibited in their complete life-histories. I illustrated my 
conception of the Protean or pleomorphic character of Bacterian 
species by a reference to the similar character of the species of 
Calcareous Sponges, and I had in my mind also the closely 
parallel facts established by Carpenter in relation to the endless 
variety of forms of the Protozoic Foraminifera. 
My view was no merely speculative suggestion, but was 
based upon a careful study of a remarkable peach-coloured 
Bacterium, which exhibited a wide range of forms, connected 
by intermediate forms, growing together in the same vessel, 
and linked to one another most unmistakeably by the fact that 
they all were coloured by a special pigment which I studied 
with the spectroscope, and to which I gave the name “ Bacterio- 
purpurin.” I observed this organism on many different occa- 
sions from various localities ; I figured and described its various 
form-phases ; I obtained some modifications of form by culti- 
vation, but chiefly depended upon the association of the 
different forms, the presence of completely transitional forms, 
and the common bond of the pigment, for the view as to their 
nature which I put forward. I gave the name Bacterium 
rubescens to this pleomorphic, or, as I termed it “ Protean,” 
species. I gave an account of further observations on this 
organism in the ‘ Quart. Journ. Micro. Sci.,’ 1876, pp. 27-40. 
Cohn opposed my view as to the genetic connection of the 
various forms associated by me under this name, and, contrary 
to the established laws of nomenclature, substituted a manu- 
script name in one of Rabenhorst’s collections (viz. roseo- 
persicina), for the duly-published name applied by me to 
this organism. He further describes some of its form-phases, 
