PARASITES OF SIMULIUM LARVAE 67 
Microscopic structure. If a portion of one of these milk white 
masses be dissected and placed in a drop of water under a cover 
glass it will be seen with the high power of a microscope to 
consist of many different minute bodies, the most abundant in 
late stages being small aggregates of eight short-oval spores 
(pl. 2, fig. 11). If the cover glass be gently pressed these aggre- 
gates will open up and take on an appearance like that shown 
in plate 2, figure 12. By gently rolling these aggregates between 
the cover glass and the slide they éan be broken up and the now 
separated spores are seen to be nearly uniform in size, short 
elliptical in shape and to measure about 3 x 2.5 — 2.7y. If 
weak iodine solution be added to the water in which they are float- 
ing a few of them will eject a short filament measuring about six 
times the length of the spore (pl. 2, fig. 18). 
Life history. In order to trace the developmental stages of this 
parasite, sections not over 5u thick must be prepared and stained, 
preferably with iron haematoxylin and orange-G. The earliest 
stages, viz., the planont and early meront, are still unknown, 
but I shall attempt to trace their conjectural development in a 
later paragraph. 
Myzxosporidium. At the time of discovery of the parasite the 
mass of meronts, or, as this is now better termed, the myxo- 
sporidium, consisted of a multinucleate mass of protoplasm meas- 
uring some 2 to 3 mm. in length, in which no definite ectoplasm 
and endoplasm could be distinguished. The central, and larger, 
portion of the myxosporidium had already sporulated and con- 
tained ripe spores; surrounding this area were all stages of devel- 
opment up to the as yet almost undifferentiated thin layer of 
protoplasm which still persisted around the edges of certain parts 
of the mass and represented all that was left of the true meront 
stage. In the stained section there is a very definite differen- 
tiation between the ripe spores and the early stages, for the 
former stain very intensely with haematoxylin, whereas the lat- 
ter are left practically unstained by this, though showing a 
marked affinity for the orange-G, so that the section takes on 
the characteristic appearance shown in plate 2, figure 2. 
Sporonts. These are typically formed by the condensation of 
the myxoplasm around the numerous nuclei of the myxosporid- 
