of Forficula auricularia. 337 
March 14—16: hatching took place, and the young were fed 
on potato and flower petals. 
August 20: 4 became adult. 
(In 1912, April 28, Mr Williams found two very small and 
apparently newly hatched young, and by August 28 both were 
adult. They lived till about March 17, 1913) 
The table of results obtained in the Cambridge Laboratory 
shows that out of about 130 Round Island females 21 certainly laid 
eggs (probably more did so and the fact escaped observation, but 
the examination of the cells was sufficiently frequent to render it 
unlikely that more than a very few clutches were missed). Four 
of the broods observed produced adult earwigs. The adults were 
nine in number, one male and eight females, which is curiously 
near the proportions given by Round Island earwigs collected in 
large quantities. The usual number of eggs laid by one female 
may be calculated very roughly by taking the average of 37, 19, 
and 12, the instances in which the eggs were counted with 
approximate accuracy; this average is 23 and is about the number 
usually found. Supposing that all the 1830 females which were 
put into cells had laid 23 eggs each, there would have been 2990. 
Actually, 21 females laid eggs, and if 283 was the average number, 
potentially 483 adults were produced. But only nine were actually 
found; which is 1:86 per cent. producing adult individuals of all 
the eggs laid. Supposing that all the 130 females which were 
isolated in cells had each laid 23 eggs, that all had hatched and 
all the young had reached maturity, 2990 adults would have been 
produced : nine in 2990 is 0°3 per cent. So great a failure to lay 
eggs at all and so great a mortality in infancy as appear in this 
case might be attributed to the artificial conditions under which 
the females were placed in October and continued in for five 
months or more before they began to lay: the conditions of 
moisture, ventilation, diet and the substances they lived among 
were all more or less abnormal. On the other hand, is it likely 
that the mortality among the immature is to any high degree less 
among earwigs in the wild state? I am inclined to doubt it. 
Again, in the artificial conditions of a laboratory the eggs and 
insects were out of the reach of various factors, both physical and 
organised, which affect adversely their development under natural 
conditions. On the other hand it seems probable that the artificial 
conditions had something to do with the great failure to lay eges, 
only 21 doing so out of 130 females presumably fertilised seems 
a very low proportion. Still, a certain number died in the first 
two or three weeks of their life in the cells, some may never have 
been fertilised and the new conditions may have inhibited the 
power of laying. As regards the failure of several of the clutches 
to hatch, the premature oviposition probably brought about by the 
