Aside from Nosema bombycis Nageli, no other Microsporidian has received so much attention of investigators as Nosema apis Zander. A disease of adult honey bees for which the Microsporidian is responsible, and which is known by different names such as Nosema-Seuche, Isle of Wight disease, Nosema disease, etc., has been reported to occur in various parts of the world. In North America, White (1914) found 40 infected bees in 120 samples received from 27 states of the union, and two diseased samples received from Canada. The same author further published (White, 1919) valuable results of experiments on the means by which the spores may be killed. The morphology and development of the Microsporidian have, however, been studied by but three investigators, i. e., Zander (1911) and Fantham and Porter (1912). According to these authors, the spores of Nosema apis are on the whole similarly constructed to those of Nosenma bombycis studied by Stempell (1909). Recently, I had an opportunity of studying the Microsporidian, and have obtained more or less different results by observations upon the structure of the spore from those of the above mentioned European investigators. I shall briefly describe the results in the following pages. In a field at Spring Valley, New York, 660 workers of Apis millifica were collected from August 27 to September 5, 1920. Although I could not trace the hive for these captured bees, there were a number of hives in the nearby woods where the collection was made. The digestive tract of each bee was drawn out from the body by means of a pair of forceps and a needle. A part of the ventriculus was smeared on a slide and examined microscopically in the fresh state.