166 The American Naturalist. [February, 
regarded the insect as dead and my observation a failure. Neverthe- 
less, on examination with the microscope, I observed that the extruded 
matter was formed of a large number of little ovoid bodies, which im- 
mediately began to move about and unroll themselves. Each of them 
was a little larva, which was very active and began to swim about. 
Were these Ephemerz viviparous? This was the question that I at 
once asked myself. Then I examined the contents of a large number 
of individuals, and I found eggs in every stage of development ; in some 
the segmentation was but slightly advanced, but a commencement of 
evolution was very distinct; in others, the extruded larvæ showed seg- 
mentation; the most advanced enclosed completely developed larvae, 
but still enclosed in the transparent membrane of the egg. I have 
since been able to observe the females emitting their larve freely with ` 
out any pressure, so that their viviparity is a proven fact. When the 
moment approaches that the insects seek the water, they allow them- 
selves to fall into it and float on the surface, with their wings extended, 
up to the moment at which the larve are extruded. During this opera- 
tion, which lasts for a very short time, the whole of the last three seg- 
ments of the abdomen are lifted upwards so as to form almost a right. 
angle with the rest of the body. The larve are expelled by a double 
orifice pierced between the seventh and the eighth abdominal rings; 
these two openings are only separated from one another by a very 
slight portion of tissue, and generally break into one another so as o 
become one after the deposition of the egg. There results a large slit 
which involves the whole of the lower half of the line of junction of 
these two rings. In this case the digestive tube is burst so that the 
nerves are detached behind the last nervous ganglion which occupies 
the seventh abdominal ring. These observations led me to study the ~ 
female genital apparatus, which ought to be constructed with a view to 
the internal development of the eggs. Almost the whole of the body 
of the female is occupied by two sacs attached, the one to the other, 
along the middle line; the vertical partition which separates them 18 
traversed by numerous tracheæ. These sacs extend over the whole 
abdomen, with the exception of the last two segments, and reach as far 
as the head, occupying in the three thoracic rings almost the whole of 
the space left free by the muscles of the wings and legs. Beneath them 
is the digestive tube, reduced to a canal with a thin and delicate W 
and the nervous chain. These two sacs open on the outside, each by ® 
distinct orifice pierced in the membrane which joins the seventh ubdom- 
inal ring to the eighth, and, as already described, at the moment of the 
quantity of greyish matter to exude from the abdomen of the animal; I 
