12 



BULLETIN OF THE BUREAU OE EISHEEIES. 



roof. Last of all she finished the mast, and while doing this she kept her wing covers 

 separated enough to supply herself continuously with fresh air. The triangular 

 plate and the mast were of the same bright yellow as the eggs and remained this 

 color for several hours. 



The whole process lasted only 1 hour and 20 minutes, and the actual time 

 consumed in spinning and egg laying was exactly 1 hour. The completed egg case 

 is ellipsoidal in shape, the roof and floor somewhat flattened, and the side walls 

 strongly convex. One end is tightly closed and the other has a lunate opening 

 beneath the triangular plate, which gives free access to the space beneath the egg 

 mass. The triangular plate is narrowed above into the mast, which rises vertically 

 about 10 mm. above the roof of the case and tapers to a rounded point. On cases 

 found floating in the pond both the triangular plate and the mast are dark brown 

 in color, almost black, due to the action of the sunlight upon the silk. 



The mast has been represented as a small tube with dense walls, whose sug- 

 gested function is the admission of air into the egg chamber. Miger and Lancret 

 (1809, p. 442) said: 



It is a mistake to suppose that the turned-up point of the cocoon serves as a mast. It is not unlikely 

 that the drawn-out point serves for the supply of air to the cocoon. 



Lyonet (1832) confessed: 



I do not know the use of this little mast. Perhaps it enables the insect to get rid of an excess of 

 silky matter. 



Laker (1881, p. 82) wrote: 



The spike consists of a substance somewhat thicker and stronger than the rest of the cocoon and ia 

 hollow throughout the greater part of its length, except that it is crossed and recrossed inside with a 

 dark, threadlike substance, thus somewhat resembling a horn stuffed with tow. 

 The apex of the spike does not, however, appear to terminate in an orifice, 

 but is closed. It does not seem to me that this spike can serve as a balance 

 to the cocoon, because the nests are usually attached to some kind of support. I 

 may, however, mention that I cut off the spike from two of the cocoons, and in 

 both these cases the eggs did not hatch. It is, however, possible that this may 

 have arisen from some other cause, although these particular cocoons ap- 

 mast of egg case, showing peared to be similar in every respect to others of which the eggs matured in 

 how the edges are rolled due course. The cocoons from which the spikes were removed subsequently 

 back to form an open gank. These nests are SO constructed that when floating loose the spike retains 

 its proper position, and even if the cocoon be held so that the spike is par- 

 allel with the water, and then suddenly released, it immediately rights itself. If, however, the spike be 

 partially submerged and then released, the cocoon turns bottom upward. 



In the six egg cases examined by the present author the mast or spike is not a 

 tube at all, but a thick flat layer of closely woven silk, whose edges curl backward 

 and almost meet along the side next to the body of the case. In this way a partially 

 closed tube is formed, but there is a narrow slit running its entire length which 

 manifestly disqualifies it from serving as an air tube (fig. 4). Furthermore, as 

 Laker says, it is closed at the apex, and we may now add that it is also closed at 

 the base, affording no connection whatever with the inside of the case. This fact 

 does not seem to have been noted by any of these observers, but it disposes once 

 for all of the supposition that the mast has anything to do with supplying air to 

 the eggs. 



