A NUTRITIONAL STUDY OF INSECTS O 



on which they leave little depressed spots where they have regur- 

 gitated and sucked up the dissolved substance. If the medium 

 has not dried enough to have taken on a hard, leathery crust, the. 

 females oviposit after twenty-four hours and continue to do so for 

 some days. The eggs are thrust into the agar so that the upper 

 end with its two projecting floating structures is just level with 

 the agar; in this position they are prominent objects under the bi- 

 nocular. After a period of one or more days, the minute larvae 

 leave the eggs and move about over the surface of the medium. 

 They are at this time usually 1.2 mm. in length. By the second 

 day they have increased in size to 1.8 to 2 mm. in length, and be- 

 gin to work in a vertical position, with the anterior end down, the 

 full length of the body in the jelly, and the posterior end with its 

 two projecting spiracles either in contact with the air or with a 

 bubble of air which has been enclosed in a thin film of the medium 

 and remains attached to the larva, thus enabling the latter to 

 work the food material to a greater depth than its body length 

 would permit. The head end of the larvae is merely a small 

 pointed segment which served as a collar through which the 

 pseudo-maxillary apparatus works. In shape the latter may be 

 roughly compared to a plow with the shares prolonged posteriorly in- 

 to two handles. Attached at the anterior end of this four-pointed 

 median structure, is a pair of deflected falcate processes, sharp at 

 the point and on the concave side, that work up and down con- 

 stantly with a simultaneous backward and forward movement of 

 the whole apparatus. The movements of these oral organs were 

 observed in a drop of agar on a depression slide, and it was found 

 that their constant movement continued without any appreciable 

 rest periods. Occasionally the movement would stop without 

 apparent reason for about two minutes, but there was no regu- 

 larity in these periods of cessation. The larva might work for 

 fifteen minutes without stopping or might stop several times at 

 intervals of two or three minutes. Apparently the recovery 

 from fatigue takes place in the interval between the movements. 

 Progression of the larva seems to be due to a series of protrusions 

 of the anterior end with an accompanying circular contraction, 

 the animal being held in place by the circles of spines on each seg'- 



