acid and imbedded in Araldite at Darajani and transported as completed blocks. In the previous study material had been sent from San Antonio in Texas to Oxford in 70 per cent alcohol after fixation. The tissues examined in the present investigation were in general much better preserved and it seems clear that when material for electron microscopy has to be transported over considerable distances it is desirable, if possible, to arrange for the imbedding to be carried out at the place where the animals are killed, even when, as in the present case, the conditions under whicl imbedding has to be carried outt are far from ideal.