148 THE ZOOLOGIST. 
spines. The spiracles along each side are brown. The legs 
number twenty. There are three pairs of thoracic legs (true legs), 
which are black, and seven pairs of abdominal legs (pro-legs), which 
have the colour of the under side of the body. The head is followed 
by twelve segments—1, 2, and 3 are thoracic segments, and each 
bears a pair of legs; 4 to 12 inclusive are abdominal joints ; 4 has 
no legs; 5, 6, 7, 8, 9, and 10 have each a pair of pro-legs; 11 has 
no legs ; and 12, the last jotnt, carries a pair of pro-legs. Before 
the first moult the head and thoracic legs are green. Hewitt 
states that there are five ecdyses and therefore six larval stages. 
The larve hatch out in eight to ten days after the eggs have 
been deposited. The larval life lasts from three to four weeks. 
The cocoon measures less than half an inch in length. It is 
brown in colour and cylindrical in shape, with rounded ends. 
The caterpillars spend the winter in the cocoon, and pupate 
about three weeks before their appearance as the imago. 
The flies are very erratic in their appearance, the earliest 
being seen at the beginning of May, and they have also been 
recorded as late as the end of July. It has been suggested that 
there are two broods, but this is certainly not the case. The 
females, which reproduce parthenogenetically (without the inter- 
vention of the male), deposit their eggs, soon after emergence, 
in the shoots of the year, these offering less resistance to the 
ovipositor than the older growth. Usually the eggs are laid in 
two parallel rows, the eggs of one row alternating with those of 
the other. Occasionally they are laid in a single row. From 
twenty to forty are deposited. 
Prof. Peck* has an interesting paragraph on the saw of these 
flies; it is as follows :—‘‘ This instrument is a very curious 
object; in order to describe it, it will be proper to compare it 
with the ordinary tenon saw used by cabinet-makers, which, 
being made of a very thin plate of steel, requires a back to 
prevent its bending. The back is a piece of iron in which a 
narrow and deep groove is cut to receive the plate which is fixed. 
The saw of the Tenthredo is also furnished with a back, but the 
groove is in the plate, and receives a prominent ridge of the 
back, which is not fixed, but permits the saw to slide forward or 
backward as it is thrown out or retracted. The saw of artificers 
* Quoted in ‘ British Insects’ by E. F. Stavely, p. 162. 
