940 LIFE : OUTLINES OF GENERAL BIOLOGY 



features in development. Again, there may be phases of adap- 

 tive value, as for lying low in times of cold or drought; and again 

 for fertilisation. This has been referred to in connection with the 

 cell-cycle (q.v.). Our thesis is simply (a) that the existing classifica- 

 tions of the Protozoa show a number of classes, which we interpret 

 as each characterised by a predominance of one of the main physio- 

 logical alternatives and its corresponding form- type of cell-life; 

 (b) that this predominance is not necessarily exclusive, but simply 

 more fully acquired in some forms than others. 



Thirdly, the critic may raise the difficulty that the class of Ciliated 

 Infusorians (Ciliata) is morphologically far removed from the class 

 of Flagellate Infusorians (Flagellata or Mastigophora), beside which 

 they should be ranked if the proposed physiological-aetiological 

 interpretation is sound. In short, the systematists have abandoned 

 the class Infusoria, pointing, for instance, to the fact that all Ciliata 

 have dimorphic nuclei (Heterokaryota), whereas the Flagellata, 

 like the Rhizopods and Sporozoa, have one kind of nucleus (Homo- 

 karyota). Our answer is simply that we have always maintained 

 the distinction between the classes Flagellata and Ciliata, and seen 

 that the two classes are not nearly related : or even of monophyletic 

 origin. We simply see both as representing an accentuation of the 



highly active habit of life; with a metabolic ratio ( ^ ), in which 



the katabolic processes lag much less markedly behind the anabolic 

 ones than is the case in Rhizopods, and a fortiori in Sporozoa. We 

 admit, of course, that we are at present so far arguing by analogy 

 when we say that a Slipper Animalcule, one-hundredth of an inch 

 long, is living more nearly up to its income than an Amoeba of the 

 same size. For quantitative measurements at this low level are not 

 easily made. 



Yet a common Amoeba moves at the rate of 600 microns per 

 minute, so that it would take towards three-quarters of an hour to 

 traverse an inch, while Paramoecium, with its specialised cilia, could 

 do this within a minute. It is doubtless at less physiological cost — 

 that of swimming compared with creeping — that the Paramoecium 

 traverses its inch, that is with less katabolism for that particular 

 piece of work; but there can be little doubt in anyone's mind that 

 the Paramoecium compared with the Amoeba is the more active 

 type; though he may not describe it in these physiological terms 

 as a predominantly katabolic one. 



Once more the critic may argue that Sporozoa are sluggish and 

 rich in anabolic reserves because they are parasitic ; that the Flagel- 

 lates and Ciliates are active and agile because the majority are 

 adapted to swift pursuit of food; and that many Rhizopods are 

 adapted to gliding along on solid surfaces and that they have often 

 to carry a relatively heavy shell, while others with vacuolated 



