ME TAMORPHOSIS. 
159 
But these are not all the marvellous changes which 
take place. The cranium ceases to grow in the larva 
before it changes to a chrysalis, while the segments of 
the body still continue to increase in size. The parts 
which are to form the head of the future nymph 
continue to grow beneath the unyielding cranium, 
from which, as the change approaches, they become 
detached, are developed backwards, and encroach 
upon the anterior portion of the first segment, the 
parts in the immediate vicinity being arrested in their 
development. This segment constitutes the atrophied 
pro-thorax of the insect, and is the first after the head. 
But at the same- time it is encroached upon by the 
second from behind, the meso-thorax, which supports 
the organs of flight. The third segment from the 
same cause is developed backwards, and the fourth, 
reduced to a very small size, exists only as the petiole, 
which connects the thorax with the abdomen. The 
fifth segment is the first true one of the abdominal 
region, and the last three are fused into one, leaving 
three segments for the thorax and six for the abdomen, 
out of the original thirteen. In the drone there is an 
additional segment. While this is going on internal 
changes take place. In the larva the spiracles are 
simple, and there are eleven on each side (Girdwoyn, 
49). In the pupa the tracheae develop in great 
numbers, and as Leydig and Weismann (168) have 
shown, they are formed by invagination, and at the 
time of casting the skin the tubes are thrown off 
with it. The silk glands disappear, and others des- 
tined for other purposes take their place. 
