TRANSACTIONS OF SECTION D. 515 
structure of the bristles and hooks is precisely the same. Both kinds likewise 
freely give rise to buds, though in regard to the appearance of the male and female 
reproductive elements in these there is room for further investigation. Thus, in 
the southern non-operculated form the buds show male elements in the front of 
the posterior region, and female elements near the tail, and after peru the 
conspicuous reddish ova are soon in evidence, the male elements, however, in 
some having previously reached maturity. Further investigation is necessary in 
connection with those having numerous small ova (North Sea) and those in 
which the ova are larger and with trochophores in the tubes. 
Finally, in forms having such a tendency to vary in plastic organs like the 
branchial pinne and the tips of the filaments, and which have or have not oper- 
cula, yet in which the general structure internally and the minute characters of 
the bristles and hooks do not vary, hesitation is felt in making a separate species 
of any type hitherto examined. 
4. On the Development of the Mesoderm and Head Kidneys of 
Pomatoceros. By Dr. C. SHmarEr. 
——s - 
5. The Isle of Wight Disease of Bees (Microsporidiosis). 
By H. B. Fanruam, D.Sc., B.A., and ANNIE Porter, D.Sc. 
The cause of ‘Isle of Wight’ disease in bees was discovered by the authors 
in 1906 to be the minute Microsporidian parasite Nosema apis. The disease is 
now known to be more widely distributed and is termed Microsporidiosis. 
Nosema apis is, in the main, a parasite of the alimentary tract of the bee, but 
can invade the hemocoel and multiply therein. Spores of the parasite swallowed 
with food or drink by the bee give rise each to an amceboid parasite, the planont, 
which parasitises either an epithelial cell of the gut or else reaches the hemocoel. 
In either case it becomes rounded, grows and feeds for a time, and then com- 
mences to multiply. The process of multiplication is termed merogony, and the 
dividing form is called the meront. Daughter meronts are formed by various 
types of binary fission producing clusters or chains. Each daughter meront is 
ultimately uninucleate. The meront stage of the parasite is often deadly to the 
host, when the parasite itself cannot attain its full development, the spore. 
The second stage of the Nosema life-cycle, known as sporogony, serves for the 
transference of the parasite to new hosts. The full-grown meront becomes the 
pansporoblast, which undergoes complicated nuclear changes whereby five nuclei 
are ultimately produced. The sporoblast also forms two vacuoles, an anterior 
polar capsule and a posterior vacuole in which the polar filament is coiled. The 
secretion of the sporocyst converts the sporoblast into the spore. The great 
power of merogony compensates for the formation of but one spore from the 
pansporoblast. Merogony causes derangement of the bee’s digestive processes. 
The symptoms of Microsporidiosis vary. Inability to fly, crawling, disloca- 
tion of the wings, abdominal distension, and “dry dysentery,’ followed by early 
death, may be noted. Warm, bright weather favours the bee, wet or damp aids 
the parasite. Bees weak after hibernation rapidly succumb. 
Nosema apis has been proved fatal by feeding hive bees, mason bees, and 
wasps on honey containing Nosema spores, some honey being artificially infected, 
other sets being naturally infected by faeces of former victims; by smearing 
infected excrement on healthy bees and allowing them to clean themselves; by 
uniting healthy and infected bees; by housing healthy bees in cases in which 
infected stock had travelled. 
In Nature the method of infection is contaminative. Hives, comb, capped 
and uncapped honey and pollen from comb have all been found to contain Nosema 
spores. Bees’ drinking-places infected with Nosema spores have been observed. 
Flowers, water from foliage, and dew from low plants near infected hives all 
have contained spores. Wind can act as a distributor of Nosema spores, also 
ants and wax-moths. Some bees can adapt themselves somewhat to the para- 
site, which forms crops of spores within them. Such parasite-carriers act as 
reservoirs of disease. 
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