516 TRANSACTIONS OF SECTION D. 
Preventive measures seem of most value in treating the disease. The only 
certain destructive agent for Nosema spores is fire. All dead bees should be 
burned. Old comb and hives untreated by a painter’s lamp after disease are to 
be avoided. Weak stocks should not be united. Great care should be exercised 
in importing bees whether from other places in the British Isles or abroad. 
Liming the soil around each hive is of service. Provision of abundant honey 
and pure water supply, together with scrupulous cleanliness of the hive and its 
surroundings, are great aids in the prevention of Microsporidiosis. 
References. . 
Fantham and Porter (1911), Proc. Zool. Soc. Lond., p. 625. : ; 
Fantham and Porter (1912), Supplement to Journ. Bd. Agric., May 1912. 
Fantham and Porter (1912), Annals Trop. Med. and Parasitology, vi., 
pp. 145-214, three plates. 
6. Some Observations on. Boring Mollusca. By B. Lrnpsay. 
In view of the part played by the work of boring mollusca as a factor in 
the process of coast erosion, it is desirable to ascertain the rate at which they 
remove the material in which they bore. But, while we know the size of the 
holes they make, we do not know how long it has taken to make them, because 
we do not know with any exactitude the age of the animals we find in the holes. 
Many attempts have been made to estimate the rate of growth of shellfish, by 
means of marks where growth has (ea hypothesi) stopped during the winter 
season. But the boring mollusca having formed themselves a shelter from the 
weather, their shells do not, as a rule, show any very definite marks of this 
kind. 
_ But the growth of successive ridges, being intimately connected with the 
periods of activity in boring, afford some clue to the rate of shell-growth. When 
boring molluscs are removed from their holes and kept loose in a tank for scme 
time, abnormalities in the margin of the shell appear, corresponding to the growth 
put on during captivity. A study of these suggests that there is a connection 
between lunar or tidal periods and the formation of new ridges; and the study 
of other bivalve molluscan shells, not borers, tends to confirm this view. 
7. The Presence and Absence Theory Unsound. 
By Dr. James: Wiuson. 
The Presence and Absence Theory originated at the time the inheritance of 
certain fowls’ combs was being studied, and was first used to explain some of the 
experimental results in that case. The experimenters took the view that rose, 
pea, and single combs are each due to an independent single factor, whereas each 
is due to two factors at least. As a matter of fact, it can be shown that there 
are four factors concerned in the production of each of the combs concerned. 
Besides, the solution of the presence and absence theory requires two factors 
to each comb, although this is not apparent until it is discovered that factors are 
made to work negatively at one time and positively at another; the facts of the 
case which the theory was set up to explain being otherwise than they were taken 
te be and the working of the same factors negatively and positively discredit the 
theory. ; 
But it is unsound on its own merits. The following may be taken. as the 
usual statement of the theory :.‘ All observations point to a conclusion of great 
importance—namely, that a dominant character is the condition due to the presence 
of a definite factor, while the corresponding recessive owes its condition to the 
absence of the same factor.’ This statement is ambiguous. If it means that a 
long factor turns a short pea into a tall, and that, by the removal of the long 
factor, the long pea becomes short again, but that the short pea is still due to the 
same original cause that made it short before the introduction of the long factor, 
there need be no quarrel with the statement further than that it does not state 
the whole case. : 
But this is not the usual interpretation—probably because of the incompleteness 
