(1) Amœboid germ with a vacuole {(a) With two polar capsules.-- the contents of which do { _Myxidiidæ._ not stain with iodine. {(b) With four polar capsules.-- _Chloromyxidæ._ (2) Amœboid germ with a vacuole stainable with iodine. Spores with two polar capsules.--_Myxobolidæ._ For further subdivisions the differences in the spores are principally utilized. Order. *Microsporidia*, Balbiani. These are the organisms discovered in the stickleback by Gluge in 1834, and in _Coccus hesperidum_ by Leydig in 1853. They have since been found in numerous other arthropods, especially insects. They acquired particular importance when it was discovered that they were the cause of the “pébrine” disease (“gattina” of the Italians) which caused so much destruction amongst silkworms (_Bombyx mori_). Pasteur (1867–70) and especially Balbiani (1866) participated in the researches on _Nosema bombycis_, and it was the latter who classed the “pébrine bodies” or “psorospermia of the arthropoda” amongst the Sporozoa as Microsporidia (1882).[223] The complete life cycle of _N. bombycis_ was described in 1909 by Stempell. The Microsporidia are not confined to insects and arachnoids, they are now known to occur also in crustacea, worms, bryozoa, fishes, amphibians and reptiles. Certain tumours in fishes, similar to those formed by many Myxosporidia, are produced by Microsporidia. Fantham and Porter found that _Nosema apis_ was pathogenic to bees and other insects, and was the causal agent of the so-called “Isle of Wight” disease in bees[224] in Great Britain. [223] _C. R. Acad. Sci._, Paris, xcv, p. 1168. [224] _Annals Trop. Med. and Parasitol._, vi, pp. 145–214, 3 pls. The Microsporidia, as their name implies, form minute spores which usually are oval or pear-shaped. Each spore contains a single polar capsule which is not easily visible in the fresh state (fig. 98, _f_) and a single amœboid germ issues from the spore (fig. 99, _b_). [Illustration: FIG. 98.--_Nosema apis._ Various stages in life-cycle. _a_, planonts or amœbulæ from chyle stomach of bee; _b_, amœboid planont creeping over surface of gut epithelial cell; _c_, uninucleate trophozoite within epithelial cell; _d_, meront with nucleus divided into four, about to form four spores; _e_, epithelial cell crowded with spores; _f_, young spore; _g_, spore showing five nuclei, polar filament ejected, and amœbula, about to issue. × 1,500, _a-e_; × 2,150, _f-g_. (After Fantham and Porter.)]