Pink Monads and their Enemies. 95 



may require ; for how can any reasoning be sound when based 

 merely on the appearances of the markings under the micro- 

 scope, which, as I have endeavoured to show, may be entirely 

 due to the peculiarity of the illumination, and may give not 

 the least indication whatever of the true structure ? 



PINK MONADS AND THEIR ENEMIES. 



BY HENEY J. SLACK, E.G.S., 

 Member of the Microscopical Society of London. 



It is no disparagement to Ehrenberg's genius and industry 

 to say, that the group of Monads (Monadina) contains ob- 

 jects that must be entirely re-arranged. Most of them are 

 plants, not animals, and many are probably only rudimentary 

 forms. In the last edition of Pritchard's valuable work, Dr. 

 Arlidge treats the Monads as belonging to a family called 

 Phytozoa, composed, as the name indicates, of "plant-like 

 animals." An arrangement of this sort can only be provisional, 

 because many of the objects do not present any animal cha- 

 racteristics, as the mere power of locomotion cannot be con- 

 sidered to deserve that name. The so-called Phytozoa com- 

 prehend Monadina, cryptomonadina, hydromorina, volvocina, 

 vibrionia, and astasia. The extreme minuteness of many of 

 these objects, and the very small size of their parts, or organs, 

 rendered it impossible that many details could be made out 

 with the object-glasses used by Ehrenberg or Dujardin, and 

 hence we need not be surprised that the former made the 

 mistake of supposing that they possessed a plurality of sto- 

 machs, or that the latter found himself unable to do more than 

 suggest artificial appellations, intended merely to facilitate 

 their recognition. The Monad group is divided into two 

 portions, one consisting of isolated individuals, and the other 

 of aggregated individuals. The former are named according 

 to their possessing one or more vibratile filaments and the 

 position in which they are placed ; the latter are either always 

 free, or at some portion of their life attached by a stalk. 

 Such an arrangement is evidently artificial, as aggregate 

 groups may, and in many cases do, result from single indivi- 

 duals or spores. 



A source of difficulty to students of these organisms arises 

 from the confusion between old and new modes of treating 

 them. Ehrenberg, as we have said, thought them all animal, 



