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Dacnusa areolaris Nees, etc. 
(Coleoptera), occasionally attacks another and larger larva of the same group 
(? Timarcha). The flies bred from the latter host are so much larger than the 
type, that they have been described as a variety, Meigenia floralis var. major. 
Inversely, examples of Thrixion holidaynum, reared from a small phasmid, 
are smaller than the type, which is parasitic upon a larger species of the same 
genus. 
This segregation could become permanent only if one form is structurally 
or physiologically compelled to oviposit in a host resembling that from which 
it was itself reared. Otherwise its offspring would revert to the grand-parental 
type. 
In the Phytomyza + Dacnusa complex, the correlation between the cessa¬ 
tion of growth and metamorphosis of the host, and the inauguration of post- 
embryonic development of the parasite, insures not only that the latter shall 
be provided with sufficient food to carry it through its transformation, but 
also that the imago shall approximate to the mean size of the race. 
NOTE ON CHALCID PARASITES OF PHYTOMYZA AN GELT CAE. 
At the beginning of August, collections of Phytomyza angelicae showed that 
while there was still considerable infestation by D. areolaris, 80 per cent, of 
the fly larvae had been parasitised or epiparasitised, as the case might be, 
by certain ectoparasitic Chalcids. Dr Luigi Massi of Genoa kindly examined 
examples of the three forms obtained, and referred them to the genera 
Chrysocharis, Eulojphus or Hemitarsus of the sub-family Eulophinae, some of 
which are known to be parasites of Phytomyzinae. 
The larvae feed externally upon the host, and are of the usual type of 
Chalcid larva. The body is 13 segmented, and the head is furnished with two 
tactile processes. At first there are four pairs of open spiracles, but when fully 
fed there are nine, namely on segments 2-10 (Fig. 5). 
As development proceeds, the larvae increase in size, but do not change 
materially in form. The host dies soon after the parasite has begun to feed, 
and in five or six days only the empty skin is left, together with the calco- 
spherites, or crystalloid concretions of certain cells of the fat body. These 
Chalcids weave no cocoon, but undergo metamorphosis within the blister on 
the leaf. The pupal period is about four weeks. 
SUMMARY. 
1. Dacnusa areolaris Nees is a parasite of the fly Phytomyza angelicae Zett. 
2. The egg is laid and development takes place within the body of the host. 
3. A membrane of trophic cells is formed, within which the embryonic 
and first larval stages are passed. 
4. The further growth and development of the parasite are delayed until 
after metamorphosis of the host, probably to ensure sufficient food in the later 
stages. 
