PROTOZOA AND OTHER ANIMALS 973 



others make use only of other constituents of the ingested material. 

 These two nutritional variants may be found in members of the same 

 group, as in Cerambycidae. The decomposition of cellulose may, in some 

 invertebrates, be accomplished by means of a tissue-produced cellulase; 

 in other, even related, forms it may require the action of symbiotic bac- 

 teria. It is possible, though the truth of the hypothesis remains to be 

 shown, that endobiotic bacteria and Protozoa may, in some instances, 

 benefit their hosts as a supplementary food source. There is a hypo- 

 thesis also that certain symbiotic microorganisms are a source of vitamins 

 or growth factors, or play a role in nitrogen economy. 



In all termites below Termitidae, except in certain functioning repro- 

 ductive castes, and in the roach Cryptocercus punctulatus, xylophagous 

 flagellates are exceedingly abundant in a specially enlarged part of the 

 hind-gut. These flagellates possess cellulase and cellobiase, and reduce 

 cellulose taken into their cytoplasm to dextrose. The insects possess no 

 tissue-produced cellulase, and few if any cellulose-decomposing bac- 

 teria or other fungi are present. These insects cannot live for long on 

 their usual diet or on cellulose without the flagellates, which presumably 

 release part of the dextrose or its dissimilation products for the use of 

 the host. This may be passed forward into the mid-gut to be absorbed, 

 or perhaps may be absorbed in the hind-gut. To what extent the nitrogen 

 needs of termites may be provided for by occasional digestion of Proto- 

 zoa or fragments of the cytoplasm, or by symbiotic nitrogen-fixing bac- 

 teria, remains to be determined. 



CILIATES OF RUMINANTS 



Among the most notable endozoic faunules of Protozoa are the ciliates 

 in ruminants and certain other herbivorous mammals. There are some 

 holotrichs, sparsely represented among the species of ciliates in rumi- 

 nants, but constituting an important and diversified part of the faunules 

 of the caecum and colon of the horse (Hsiung, 1930). There are also 

 a few flagellates and amoebae, but the most characteristic forms belong 

 to the Entodiniomorphina. Of the two families of this suborder of 

 highly organized spirotrichs, Ophryoscolecidae occur chiefly in rumi- 

 nants (see Dogiel, 1927; Kofoid and MacLennan, 1930, 1932, 1933; 

 Wertheim, 1935); and Cycloposthiidae are best known in the horse 

 (see Hsiung, 1930). The latter family is represented also in a number 



