Gregarina contains a large amount of osmotically inactive meterial, chiefly glycogen. In this respect it resembles other parasites such as Ascaris. It possesses no mechanism for regulating its internal osmotic pressure; therefore it quickly reaches a state of equilibrium with the medium in which it is placed. It is more permeable to substances of high lipoid solubility than to those of low lipoid solubility even though the former may have a larger molecule than the latter. In this respect it resembles other cells which have been studied, but it is more permeable than these cells to substances of low lipoid solubility and large molecular size such as glucose and fructose.

Thesis approved for the degree of Doctor of Philosophy in the University of London.