502 PROFESSOR E. RAY LANKESTER. 
collective species, his Coccobacteria septica. It received 
later a support through the views which Nageli (1877) expressed 
in the words, ‘I have investigated during the past ten years 
many thousands of Bacterian forms, and I could not maintain 
(if I except Sarcina) that there was any need for a separation 
into even two specific forms.’ Nageli, however, adds that he 
by no means maintains that all forms belong to one single 
species: it were a bold thing in his opinion to express a definite 
conclusion in a matter in which morphological observation and 
physiological experiment leave the investigator so much in the 
lurch. He expresses himself again in the same sense in 1882. 
He nevertheless is, when carefully considered, in agreement 
with Cohn’s fundamental conception, since Cohn erected his 
form-genera and his form-species (the latter based on physio- 
logical properties) primarily in order to gain a provisional 
survey, and irrespective of the question (as he distinctly states) 
as to whether as thus distinguished they correspond to natural 
species. 
“ Nageli’s words above cited contain a pregnant criticism of 
the whole controversy, so far as it had then gone. Both 
parties failed to bring forward (as is especially the case in 
Billroth’s book) the only certain basis for their opinions, 
namely, the strict observation of the continuity or the non- 
continuity of the forms or species in question. In the absence 
of this, our judgment could only remain suspended, more 
especially since the forms in question are minute, very like to 
one another, often mixed together, and consequently easily to 
be mistaken for one another in the absence of quite strict 
observation. Lankester certainly came somewhat nearer 
towards establishing a special case of strictly-observed con- 
tinuity, since the forms of his Bacterium rubescens 
(Beggiatoa roseo-persicina) gave evidence of their con- 
nection with one another more clearly by their characteristic 
colouration. Strictly-made morphological and developmental 
researches are now to hand. They have demonstrated that the 
forms known as Cocci, Rods, Threads, &c., are phases of growth 
(Wuchsformen).” 
