224 Annals Entomological Society of America [Vol. XII, 



woven silk cap or plug at the upper end of the tunnel, com- 

 pletely closing it. This plug is quite firm in texture and has a 

 thickness of about 0.7-0.8 mm. over most of its area. At the 

 periphery, where it makes contact with the side of the burrow, 

 it is reduced in thickness to an extremely fine membrane, thus 

 providing for the emergence of the imago. The greater part of 

 the burrow is then lined with a strong, silken cocoon, in the 

 upper end of which the pupa is formed. This cocoon is con- 

 nected with the above-mentioned cap by means of a vertical 

 curtain of silk. The closing plug and complete cocoon seem to 

 be effective in excluding the water and make it possible for this 

 type of pupa to successfully pass its quiescent period in a position 

 slightly below the water line. That this is an aquatic adaptation 

 is indicated by Chittenden's observation (1918, p. 456), that 

 under the terrestrial conditions of raspberry plants a "small 

 amount of silk is used in the construction of these hibernating 

 chambers, and a little is usually to be found at either end" — a 

 description which in no way applies to the same activities of the 

 larva in the Nelumbo petiole. The versatility of this larva in 

 becoming adjusted to different surroundings is manifested by 

 the fact that the writer found a few instances of pupation in 

 the rolled up edges of the Nelumbo leaf — instances in which 

 a strong, silken cocoon was formed, but no hint of any special 

 features such as the lid-like cap to the petiole burrow. Nothing 

 can be stated at present concerning the nature of the stimuli 

 or sets of stimuli which are operative in impelling the larva to 

 produce an entirely different cocoon for each of the three known 

 pupation conditions, viz., the petiole burrow, the rolled leaf 

 margin, and the stems of certain terrestrial plants. The fact, 

 however, certainly emphasized the special adjustments which 

 have been developed in connection with the aquatic conditions 

 and which have been superimposed upon a persistent ancestral 

 habit. 



While it seems evident that the closing cap at the entrance 

 to the tunnel and the underlying, strong, silken cocoon provide 

 a certain protection against drowning, they are not sufficient 

 to safeguard the pupa from another danger — the larvae of its 

 own species. It often happens that some larva, wandering 

 on the Nelumbo leaves, eats away the closing cap of a pupal 

 chamber, penetrates the upper end of the cocoon, destroys the 

 upper portion of the pupa, and ensconces itself in the re-opened 



