440 SUPPLEMENT 



whitish, with the point of a deep brown, and which, flat at 

 first upon one side, becomes rounded in drying, and tubular 

 in all its length. At its base is the aperture prepared for 

 the issue of the larva. It is closed by some threads, which, 

 by means of the air enclosed in the shell, hinder the water 

 from introducing itself. It happens, however, that some 

 eggs, placed near this aperture, are not always preserved, 

 and they become decomposed. The interior of the shell, 

 after we have removed that part opposite to that which is 

 nearest to the surface of the water, presents from forty-five 

 to fifty little cylinders, slightly inflated, and curved towards 

 their summit, of the length of two lines, grouped, in cross- 

 ing, at the middle of the shell, all in a vertical position, 

 and having each a particular lodge, formed by the cottony 

 down of which we have spoken. This down retaining the 

 eggs, is attached to the upper part of the shell, and leaves, 

 at the lower part and all around, a void space which extends 

 as far as the aperture. From this disposition of the eggs, 

 we may well conceive how the shell, a little isolated, is 

 retained upon the water in the position which is natural 

 to it. 



The egg undergoes a sort of development. It swells, 

 assumes a brown and shining tint, and it is possible to dis- 

 tinguish the form of the larva, and particularly the eyes. 

 The pellicle of the egg breaks, and we see this larva issue 

 forth, which is twice as large as the egg, and begins to stir 

 about in all directions. It disengages itself with so much 

 the more facility, because there is an empty space above the 

 head. All the larvae have this part of the body directed to 

 this side. Thither they repair at their birth, and there they 

 rest during more than twelve hours without taking any 

 nourishment, and are stirring about one against the other. 

 They leave no vestiges of the cottony cases which kept them 

 separated. M. Miger has several times observed that the 



