CONTENTS. 



PAGE. 



Introduction 



Previous work on Thompsonia 5 



Preliminary description of material 7 



The root system 9 



The structure of the external sacs 16 



Development 18 



The changes in the visceral mass during development 20 



The liberation of the Cypris larvae 21 



The formation of new external sacs 21 



Development of germ cells in the root system 23 



The social forms of Peltogaster and Thompsonia compared 24 



The evolution of Thompsonia 26 



Thompsonia and Thylacoplethus 27 



The species of Thompsonia 29 



The influence of the parasite on the host 30 



Summary 31 



Bibliography 32 



2 



