166 Mr. Poulton's tiotes in 1885 iqjon 



ones invariably dies when its increasing size brings it 

 into contact with the sides of the more developed larvse. 

 Such facts are more consistent with the view that the 

 motive force is at any rate chiefly supplied by the host. 



The largest larvte were 3'5 mm. long (but really longer 

 because of their curved position), and the contents of 

 the digestive tract were dark green. Minute white dots 

 were very obvious attached to the ramifications of the 

 tracheal system. They are probably fat-cells, and have 

 been described and figured by Newport (in the paper 

 mentioned above). The active contractions of the 

 digestive tract, mentioned by Newport, were very obvious. 

 After the first change of skin the black head- shield is 

 lost, and the head of subsequent stages is white and 

 transparent. Newport accurately describes the mode in 

 which the successive skins are shuffled down to the 

 posterior end of the body. DeGeer certainly recognises 

 the old larval skin attached to the egg-shell upon the 

 shrunken remains of D. vinula, but he does not see that 

 it is made up of more than one skin. The head is 

 somewhat easily detached from the body of the host in 

 the large parasites (3'5 mm. long), but the hold is soon 

 tightly renewed. DeGeer has made a similar observa- 

 tion. After detaching the head a small black scar is 

 seen at the point where it was fixed, but so minute that 

 no loss of fluid takes place through it. The presence of 

 several such scars close together show that the larvas 

 sometimes voluntarily vary the point of attack. 



By August 20th the largest larvae were quite 5 mm. 

 long, allowing for their curved position, and they had 

 changed their skins for the second time. The larva of 

 D. vinula was much enfeebled and flaccid, but still alive. 

 Only seven of the parasites now remained alive. On 

 the evening of the 21st the most advanced larva changed 

 its skin again, and gained a very different appearance, 

 becoming a dull white instead of glistening, and with 

 the intersegmental furrows well marked instead of the 

 previous tense and swollen condition. It also possessed 

 the row of lateral lobes spoken of by many authors. On 

 touching the larva it fell oft" and rolled about with active 

 but aimless contractions. In the natural state they 

 would be enclosed in the same cocoon with the larva, 

 and in such a narrow space the movements could not 

 take the parasites away from their food. On the 22nd 



