68 THE INVERTEBRATA 



front than behind; provided with very numerous flagella arranged in 

 three distinct sets; without gullet. At the front end is a papilla. The 

 ectoplasm, thin behind, is strong and complex in the fore part of the 

 body, where it is composed of the following layers: (i) a pellicle, 

 sculptured into longitudinal ridges, (2) a layer containing longi- 

 tudinal rows of the basal granules of the flagella, (3) a layer containing 

 a network of rhizoplasts ("oblique fibres"), (4) an alveolar layer, 

 (5) a layer of transverse myonemes, (6) a layer of longitudinal my- 

 onemes. In the conical front region on which the first set of flagella 

 stand, the rhizoplasts and basal granules are merged to form con- 

 verging strands with which the flagella are connected. At division this 

 conical apparatus acts as a division centre, dividing first and forming 

 the spindle between its halves as they separate. Possibly it does so in 

 virtue of a concealed centriole. Trichonympha is symbiotic with ter- 

 mites, in whose gut it lives (p. 435). The termite devours wood but is 

 unable itself to digest it. The digestion is performed by the protozoon, 

 which obtains in return food and lodging. Wood particles are con- 

 tained in the endoplasm of the hinder part of the body of Tricho- 

 nympha, into which they are ingested by the cupping-in of this region 

 under the action of the myonemes of the forepart. 



Class SARCODINA (RHIZOPODA) 



Protozoa which in the principal phase are amoeboid, without flagella; 

 are usually not parasitic; have no meganucleus; and, though they may 

 have a phase of sporulation, do not form large numbers of spores after 

 syngamy. 



With the exception of the Amoebina and Foraminifera, which are 

 undoubtedly closely related, the orders of this class have much less 

 affinity with one another than have those of the Mastigophora. In 

 all of them flagellate young and gametes are common. 



Order AMOEBINA 



Sarcodina which have no shell, skeleton, or central capsule; whose 

 pseudopodia never form a reticulum and are usually lobose ; and whose 

 ectoplasm is never vacuolated. 



Thus defined, the group excludes forms such as Arcella which 

 differ from its members practically only in the possession of a shell. 

 These forms, however, are also connected with the typical Forami- 

 nifera by intermediates (as Lieberkuhnia and Allogromia) . There is, 

 indeed, a continuous series from naked amoebae to such foraminifera 

 as Polystomella, and the drawing of a boundary line between the 

 groups of which they are typical is a matter of convenience. 



