1896.] 



201 



removal ; but the insect itself is of a very different form, and belongs 

 apparently to the " articulatus " group. The absence of circumgenital 

 glands indicates an ovoviviparous habit. 



Bearsted, Maidstone : 



August MJi, 1896. 



ON AKEESTED DEYELOPMENT OP PARTS IN INSECTS. 

 BY BR. D. SHARP, M.A., P.R.S. 



It is well known that occasionally specimens of insects are found 

 the head of which is that of a larva, while the other parts are in the 

 imaginal state. Some time ago I published a note showing that, in a 

 case I had observed, an abnormal combination of this kind occurred 

 as the result of injury, before metamorphosis, to the part that re- 

 mained in the larval state. Another observation I have just made 

 leads me to extend this idea, and suggest that the mixed condition is 

 generally, perhaps always, the result of injury to a part, which con- 

 sequently dies, and does not complete the metamorphosis though the 

 other parts do. A few days ago I gathered a head of wild parsnip to 

 examine a larva in it {^Depressaria heracleana, I believe), and I was 

 surprised to find that though the larva was about full-grown it had on 

 the head and thorax three or four eggs of a parasite. Wishing to see 

 what would happen, 1 took the larva home and kept it under observa- 

 tion. The eggs ou the head did not hatch, and so far as I could see 

 no change took place in them ; the egg on the thorax, however, com- 

 menced a process of sinking in, and became placed in a sort of 

 depression of the surface, but did not completely disappear, and there 

 was moisture on the surface around it. I suspected that this was a 

 sort of intermediate condition between external and internal parasitism ; 

 but as I did not wish to interfere with the natural conditions, I did 

 not ascertain whether there was a hatched parasitic larva beneath the 

 partially embedded egg. Leaving it for a few days longer, I then 

 opened the box, and was much surprised at the condition of affairs : 

 the larva had done what it could towards pupating, viz., the abdomen 

 had become pupal, but the head and thorax were still larval. Perhaps 

 I ought to have allowed the natural experiment to go on, and have 

 thus ascertained whether the parasitic larva (supposing there really 

 was a larva) would have destroyed the organism entirely ; but as the 

 experiment was not being conducted under really natural conditions, 

 I thought it probable all would die and rot ; I therefore transferred 

 the specimen to spirit, so that it may be seen by any one interested. 



Cambridge : July 2hth, 1896. 



