MICROSPORIDIA 185 



and other insects, and was the causal agent of the so-called "Isle of Wight" 

 disease in bees 1 in Great Britain. 



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, /) and a single amoeboid germ issues from the spore 

 (fig. 99, ). 



The life cycle of Nosema apis, parasitic in bees, may be taken as an example of 

 that of a microsporidian. The infection of the host is initiated by the ingestion of 

 spores of N. apis in food or drink contaminated with the excrement of other infected 



FIG. 98. A osema apis. Various stages in life-cycle, a, planonts or amoebulae from chyle 

 stomach of bee ; />, amoeboid planont creeping over surface of gut epthelial cell ; c, uninucleate 

 trophozoite within epithelial cell ; d, meront with nucleus divided into four, about to form 

 four spores ; e, epiihelial cell crowded with spores; f, young spore; g, spore showing five 

 nuclei, polar filament ejected, and amoabula, about to issue. X 1,500, a e; X 2,i$o,f g. 

 (After Fantham and Porter.) 



bees. Under the influence of the digestive juice of the bee the spore-coat (sporocyst) 

 softens, the polar filament is ejected and anchors the spore to the gut epithelium, 

 and the minute amcebula contained in the spore emerges. The amcebula is capable 

 of active amoeboid movements (fig. 98, b] and so is termed the planont or wandering 

 form (fig. 98, a). After a short time each planont penetrates between or into the cells 

 of the epithelium of the gut, a few only passing through into the body cavity. Within 

 the cells the amcebulas become more or less rounded, lose their power of movement, 

 and after a period of growth of the trophozoite (fig. 98, c] commence to divide actively, 

 these dividing forms being known as meronts (fig. 98, d\ Various forms of fission 

 occur, and during this phase, termed merogony, the numbers of the parasite within 

 the host are greatly increased, with concomitant destruction of the epithelium 

 (fig. 98, e). After a time sporogony commences. The full-grown meront becomes 

 successively the pansporoblast and sporoblast. Nuclear multiplication and differen- 

 tiation ensue and five nuclei are ultimately produced. At the same time a sporocyst 

 is secreted, and two vacuoles are produced within. One is the polar capsule, and 



1 Annals Trop. Med. and ParasitoL, vi, pp. 145-214, 3 pis. 



